Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Recombination”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 955 records · Page 53Linked to original sources
PubMed1996

Somatic recombination, gene amplification and cancer.

The principle objective of this research programme, to analyse chemical induction of somatic recombination and related endpoints, i.e., mobilization of transposing elements and gene amplification, has been approached by means of several assay systems. These have included Drosophila, Saccharomyces and mammalian cell cultures. 6.1. Screening assays for mitotic recombination. A large number of chemicals have been investigated in the three Drosophila assay systems employed--the multiple wing hair/flare wing spot system developed by Graf et al., 1984, the white-ivory system developed by Green et al., 1986 and the white/white+ eye spot assay developed by Vogel (Vogel and Nivard, 1993). Particularly the screening of 181 chemicals, covering a wide array of chemical classes, by the last mentioned assay has shown that measurement of somatic recombination in Drosophila constitutes a sensitive and efficient short-term test which shows a remarkably good correlation with the agent score of 83 short-term tests analysed by ICPEMC (Mendelsohn et al., 1992; Table 2) as well as the assay performance in international collaborative programmes measuring carcinogen/non-carcinogens (de Serres and Ashby, 1981; Ashby et al., 1985, 1988). Also the wing spot assay has gained wide international recognition as a similarly sensitive test. These two assay systems in Drosophila measure both intrachromosomal events and interchromosomal recombination. The white-ivory system on the other hand is based on the loss of a tandem duplication in the white locus, the mechanism of which is less known, but probably involves intrachromosomal recombination. The difference in the mechanism between this assay and the former two was indicated by the lack of response to methotrexate in the white-ivory assay, while this compound was strongly recombinogenic in both the wing spot and white/white+ assays. The use of different strains of Drosophila with the white/white+ assay demonstrated the importance of the background genotype for the outcome of the test. Up to a 60-fold variation was found between the different genotypes in the response to procarcinogens, evidently dependent on differences in the metabolic activation of procarcinogens. In 1989 Schiestl presented results on intrachromosomal recombination in the strain RS112 of Saccharomyces, which indicated a capability to detect a range of chemical carcinogens, which gave negative results in Ames Salmonella assay. Such a test system, which could identify a larger range of potential carcinogens than conventional short-term tests evidently would be of great value and it therefore seemed of importance to follow up the observations by Schiestl. However, studies within this programme on the same strain of Saccharomyces, as well as the strains D7 (measuring intragenic recombination, intergenic recombination, and point mutation) and JD1 (measuring intragenic recombination at two loci) could not support the observations and interpretation by Schiestl (1989). The Drosophila white-ivory system, which presumably responds primarily by intrachromosomal recombination, did not give positive results with these Salmonella-negative agents either. One system to measure mitotic recombination in mammalian cell cultures was developed in the present programme. It was based on heterozygous mutations in both alleles of the adenosine deaminase gene (ADA). The system selects for proficient recombinants generated by the deficient cells. So far only pilot experiments, indicating that this experimental system operates as planned, have been performed. 6.2 Mechanisms of mitotic recombination The induction of mosaic spots in the wing spot and the white/white+ assays is predominantly dependent on interchromosomal recombination. This is evident from the fact that heterozygous inversions reduce the frequency of spots. A relationship between the length of inversions and the reduction of spots was demonstrated in the white/white+ assay--the long inversion ln(l)sc4L

Animals↗
PubMed1980

Visualization of genetic recombination intermediates of human adenovirus type 2 DNA from infected HeLa cells.

The study of recombination in prokaryotes has been facilitated by the availability of recombinational mutants and simple genetic elements such as phages and plasmids. These small but defined molecules of DNA have been especially useful for electron microscopic analysis of structural detail of molecules undergoing recombination both in vivo and in vitro. A limitation in the structural analysis of plasmid recombination is the absolute number of recombining molecules which can be identified and analysed amidst a background of nonrecombining molecules. This limitation would be of even greater consequence in studies of genetic recombination in animal cells. We therefore chose virus-infected animal cells as a model system for the study of the molecular mechanism of genetic recombination in higher organisms. HeLa cells infected with adenovirus serotype 2 (Ad-2) offer several advantages for studying recombination: (1) the virus contains a small and well characterized genome of about 35 kilobases; (2) a large amount of Ad-2 DNA is accumulated during lytic infection and host DNA synthesis is suppressed; (3) Ad-2 recombines at a very high frequency; and (4) similar to phages, animal viruses and Ad-2 in particular are believed to use many of the host cell's enzymes in necessary metabolic processes, presumably including recombination. In this study we used electron microscopic techniques to visualize the structures of in vivo Ad-2 DNA recombination intermediates. Molecules were observed with structures at putative cross-over points which were consistent with the molecular mechanism of recombination proposed by Holliday. In addition, we observed Ad-2 DNA molecules engaged in recombination which were simultaneously serving as templates for replication and/or transcription. To the best of our knowledge, this is the first visualization of in vivo recombination intermediates of discrete DNA molecules isolated from eukaryotic cells.

Adenoviruses, Human↗
PubMed1989

Enhancement of Escherichia coli plasmid and chromosomal recombination by the Ref function of bacteriophage P1.

The Ref activity of phage P1 enhances recombination between two defective lacZ genes in the Escherichia coli chromosome (lac- x lac- recombination). Plasmid recombination, both lac- x lac- and tet- x tet-, was measured by transformation of recA strains, and was also assayed by measurement of beta-galactosidase. The intracellular presence of recombinant plasmids was verified directly by Southern blotting. Ref stimulated recombination of plasmids in rec+ and rec(BCD) cells by 3-6-fold, and also the low level plasmid recombination in recF cells. RecA-independent plasmid recombination, either very low level (recA cells) or high level (recB recC sbcA recA cells), was not stimulated. Ref stimulated both intramolecular and intermolecular plasmid recombination. Both normal and Ref-stimulated lac- x lac- chromosomal recombination, expected to be mostly RecBC-dependent in wild-type bacteria, were affected very little by a recF mutation. We have previously reported Ref stimulation of lac- x lac- recombination in recBC sbcB bacteria, a process known to be RecF-dependent. Chromosomal recombination processes thought to involve activated recombination substrates, e.g., Hfr conjugation, P1 transduction, were not elevated by Ref activity. We hypothesize that Ref acts by unknown mechanisms to activate plasmid and chromosomal DNA for RecA-mediated recombination, and that the structures formed are substrates for both RecF-dependent (plasmid, chromosomal) and Rec(BCD)-dependent (chromosomal) recombination pathways.

Bacteriophages↗
PubMed1994

Approaches to half-tetrad analysis in bacteria: recombination between repeated, inverse-order chromosomal sequences.

In standard bacterial recombination assays, a linear fragment of DNA is transferred to a recipient cell and, at most, a single selected recombinant type is recovered from each merozygote. This contrasts with fungal systems, for which tetrads allow recovery of all meiotic products, including both ultimate recombinant products of an apparent single act of recombination. We have developed a bacterial recombination system in which two recombining sequences are placed in inverse order at widely separated sites in the circular chromosome of Salmonella typhimurium. Recombination can reassort markers between these repeated sequences (double recombination and apparent gene conversion), or can exchange flanking sequences, leading to inversion of the chromosome segment between the recombining sequences. Since two recombinant products remain in the chromosome of a recombinant with an inversion, one can, in principle, approach the capability of tetrad analysis. Using this system, the following observations have been made. (a) When long sequences (40 kb) recombine, conversion frequently accompanies exchange of flanking sequences. (b) When short sequences (5 kb) recombine, conversion rarely accompanies exchange of flanks. (c) Both recA and recB mutations eliminate inversion formation. (d) The frequency of exchanges between short repeats is more sensitive to the distance separating the recombining sequences in the chromosome. The results are presented with the assumption that inversions occur by simple interaction of two sequences in the same circular chromosome. In an appendix we discuss mechanistically more complex possibilities, some of which could also apply to standard fungal systems.

Bacteria↗
PubMed1998

The M26 hotspot of Schizosaccharomyces pombe stimulates meiotic ectopic recombination and chromosomal rearrangements.

Homologous recombination is increased during meiosis between DNA sequences at the same chromosomal position (allelic recombination) and at different chromosomal positions (ectopic recombination). Recombination hotspots are important elements in controlling meiotic allelic recombination. We have used artificially dispersed copies of the ade6 gene in Schizosaccharomyces pombe to study hotspot activity in meiotic ectopic recombination. Ectopic recombination was reduced 10-1000-fold relative to allelic recombination, and was similar to the low frequency of ectopic recombination between naturally repeated sequences in S. pombe. The M26 hotspot was active in ectopic recombination in some, but not all, integration sites, with the same pattern of activity and inactivity in ectopic and allelic recombination. Crossing over in ectopic recombination, resulting in chromosomal rearrangements, was associated with 35-60% of recombination events and was stimulated 12-fold by M26. These results suggest overlap in the mechanisms of ectopic and allelic recombination and indicate that hotspots can stimulate chromosomal rearrangements.

Alleles↗
PubMed1992

Mechanisms of intermolecular homologous recombination in plants as studied with single- and double-stranded DNA molecules.

To elucidate the mechanism for intermolecular homologous recombination in plants we cotransformed Nicotiana tabacum cv Petit Havana SR1 protoplasts with constructs carrying different defective derivatives of the NPTII gene. The resulting kanamycin resistant clones were screened for possible recombination products by PCR, which proved to be a valuable technique for this analysis. Our results show that the double-stranded circular DNA molecules used in this study recombine predominantly via a pathway consistent with the single-strand annealing (SSA) model as proposed for extrachromosomal recombination in mammalian cells. In the remaining cases recombination occurred via a single reciprocal recombination, gene conversion and possibly double reciprocal recombination. Since single-stranded DNA is considered to be an important intermediate in homologous recombination we also established the recombination ability of single-stranded DNA in intermolecular recombination. We found that single-stranded DNA enters in recombination processes more efficiently than the corresponding double-stranded DNA. This was also reflected in the recombination mechanisms that generated the functional NPTII gene. Recombination between a single-stranded DNA and the complementing DNA duplex occurred at similar rates via a single reciprocal recombination and the SSA pathway.

Base Sequence↗
PubMed2004

Inter- and intralineage recombinants are common in natural populations of Turnip mosaic virus.

A recombination map of the genome of Turnip mosaic virus (TuMV) was assembled using data from 19 complete genomic sequences, previously reported, and a composite sample of three regions of the genome, one-third in total, of a representative Asia-wide collection of 70 isolates. Thus, a total of 89 isolates of worldwide origin was analysed for recombinants. Eighteen recombination sites were found spaced throughout the 5' two-thirds of the genome, but there were only two in the 3' one-third; thus, 24 and 35 % of the P1 and NIa-VPg gene sequences examined were recombinants, whereas only 1 % of the corresponding NIa-Pro and CP gene sequences were recombinants. Recombinants with parents from the same or from different lineages were found, and some recombination sites characterized particular lineages. Most of the strain BR recombinants belonged to the Asian-BR group, as defined previously, and it was concluded that this lineage resulted from a recent migration, whereas many of the strain B recombinants from Asia fell into the world-B group. Again, a large proportion of isolates in this group were recombinants. Some recombination sites were found only in particular lineages, and hence seemed more likely to be the surviving progeny from single recombinational events, rather than the progeny of multiple events occurring at recombination hotspots. It seems that the presence of recombination sites, as well as sequence similarities, may be used to trace the migration and evolution of TuMV.

Asia↗
PubMed2006

Exceptionally high levels of recombination across the honey bee genome.

The first draft of the honey bee genome sequence and improved genetic maps are utilized to analyze a genome displaying 10 times higher levels of recombination (19 cM/Mb) than previously analyzed genomes of higher eukaryotes. The exceptionally high recombination rate is distributed genome-wide, but varies by two orders of magnitude. Analysis of chromosome, sequence, and gene parameters with respect to recombination showed that local recombination rate is associated with distance to the telomere, GC content, and the number of simple repeats as described for low-recombining genomes. Recombination rate does not decrease with chromosome size. On average 5.7 recombination events per chromosome pair per meiosis are found in the honey bee genome. This contrasts with a wide range of taxa that have a uniform recombination frequency of about 1.6 per chromosome pair. The excess of recombination activity does not support a mechanistic role of recombination in stabilizing pairs of homologous chromosome during chromosome pairing. Recombination rate is associated with gene size, suggesting that introns are larger in regions of low recombination and may improve the efficacy of selection in these regions. Very few transposons and no retrotransposons are present in the high-recombining genome. We propose evolutionary explanations for the exceptionally high genome-wide recombination rate.

Animals↗
PubMed2006

Gene conversion in transgenic maize plants expressing FLP/FRT and Cre/loxP site-specific recombination systems.

DNA recombination reactions (site-specific and homologous) were monitored in the progeny of transgenic maize plants by bringing together two recombination substrates (docking sites and shuttle vectors) in the zygotes. In one combination of transgenic events, the recombination marker gene (yellow fluorescent protein gene, YFP) was activated in 1%-2% of the zygotes receiving both substrates. In other crosses, chimeric embryos and plants were identified, indicative of late recombination events taking place after the first mitotic division of the zygotes. The docking site structure remained unchanged; therefore, all recovered recombination events were classified as gene conversions. The recombinant YFP-r gene segregated as a single locus in subsequent generations. The recombination products showed evidence of homologous recombination at the 5' end of the YFP marker gene and recombinational rearrangements at the other end, consistent with the conclusion that DNA replication was involved in generation of the recombination products. Here, we demonstrate that maize zygotes are efficient at generating homologous recombination products and that the homologous recombination pathways may successfully compete with other possible DNA repair/recombination mechanisms such as site-specific recombination. These results indicate that maize zygotes provide a permissive environment for homologous recombination, offering a new strategy for gene targeting in maize.

Attachment Sites, Microbiological↗
PubMed1995

Efficient system of homologous RNA recombination in brome mosaic virus: sequence and structure requirements and accuracy of crossovers.

Brome mosaic virus (BMV), a tripartite positive-stranded RNA virus of plants engineered to support intersegment RNA recombination, was used for the determination of sequence and structural requirements of homologous crossovers. A 60-nucleotide (nt) sequence, common between wild-type RNA2 and mutant RNA3, supported efficient repair (90%) of a modified 3' noncoding region in the RNA3 segment by homologous recombination with wild-type RNA2 3' noncoding sequences. Deletions within this sequence in RNA3 demonstrated that a nucleotide identity as short as 15 nt can support efficient homologous recombination events, while shorter (5-nt) sequence identity resulted in reduced recombination frequency (5%) within this region. Three or more mismatches within a downstream portion of the common 60-nt RNA3 sequence affected both the incidence of recombination and the distribution of crossover sites, suggesting that besides the length, the extent of sequence identity between two recombining BMV RNAs is an important factor in homologous recombination. Site-directed mutagenesis of the common sequence in RNA3 did not reveal a clear correlation between the stability of predicted secondary structures and recombination activity. This indicates that homologous recombination does not require similar secondary structures between two recombining RNAs at the sites of crossovers. Nearly 20% of homologous recombinants were imprecise (aberrant), containing either nucleotide mismatches, small deletions, or small insertions within the region of crossovers. This implies that homologous RNA recombination is not as accurate as proposed previously. Our results provide experimental evidence that the requirements and thus the mechanism of homologous recombination in BMV differ from those of previously described heteroduplex-mediated nonhomologous recombination (P. D. Nagy and J. J. Bujarski, Proc. Natl. Acad. Sci. USA 90:6390-6394, 1993).

Base Sequence↗
PubMed1994

Regulation and targeting of recombination in extrachromosomal substrates carrying immunoglobulin switch region sequences.

We have used extrachromosomal substrates carrying immunoglobulin heavy-chain S mu and S gamma 3 switch region sequences to study activation and targeting of recombination by a transcriptional enhancer element. Substrates are transiently introduced into activated primary murine B cells, in which recombination involving S-region sequences deletes a conditionally lethal marker, and recombination is measured by transformation of Escherichia coli in the second step of the assay. Previously we found that as many as 25% of replicated substrates recombined during 40-h transfection of lipopolysaccharide (LPS)-stimulated primary cells and that efficient recombination was dependent on the presence of S-region sequences as well as a transcriptional activator region in the constructs (H. Leung and N. Maizels, Proc. Natl. Acad. Sci. USA 89:4154-4158, 1992). Here we show that recombination of the switch substrates is threefold more efficient in LPS-cultured primary B cells than in the T-cell line EL4; the activities responsible for switch substrate recombination thus appear to be more abundant or more active in cells which can carry out chromosomal switch recombination. We test the role of the transcriptional activator region and show that the immunoglobulin heavy-chain intron enhancer (E mu) alone stimulates recombination as well as E mu combined with a heavy-chain promoter and that mutations that diminish enhancer-dependent transcription 500-fold diminish recombinational activation less than 2-fold. These observations suggest that the enhancer stimulates recombination by a mechanism that does not depend on transcript production or that is insensitive to the level of transcript production over a very broad range. Furthermore, we find that E mu stimulates recombination when located either upstream or downstream of S mu but that the position of the recombinational activator does affect the targeting of recombination junctions, suggesting that the relatively imprecise targeting of switch junctions in vivo may reflect the availability of many potential activator sites within each switch region.

Animals↗
PubMed1989

High-level recombination specific to polyomavirus genomes targeted to the integration-transformation pathway.

An unusually high incidence of interviral recombination was found in the process of integration of the polyomavirus genome concomitant with neoplastic transformation of nonpermissive cells. Transformants were isolated after mixed infections of Fischer rat cells with two mutants lacking restriction endonuclease sites and were analyzed for the presence of unselected integrated recombinant restriction fragments. A large fraction of the transformants isolated (38% of the 64 transformed cell lines studied) contained recombinant viral genomes that had undergone recombination in a 1.3-, 1.7-, or 3.6-kilobase-pair interval. More than 90% of these recombinant transformants showed evidence of crossovers in multiple intervals. To our knowledge, the recombination frequencies observed in these experiments represent the highest frequencies of homologous recombination reported for a mitotic mammalian system that does not involve transfection. In contrast to the elevated level of recombination in the integrated viral genomes, no evidence of recombination was obtained among the replicated unintegrated pool of viral genomes isolated from the same population of infected cells from which the recombinant transformants were derived. Either of two hypotheses can provide an explanation for the segregated recombination: either recombination occurs at elevated levels in a small, recombination-prone fraction of the population destined to become transformed, or recombination occurs only among those viral genomes which are engaged in the process of integration and thus interact with a recombinogenic host machinery (for example, the host scaffold). We favor the latter hypothesis.

Animals↗
PubMed2006

Evidence of structural genomic region recombination in Hepatitis C virus.

BACKGROUND/AIM: Hepatitis C virus (HCV) has been the subject of intense research and clinical investigation as its major role in human disease has emerged. Although homologous recombination has been demonstrated in many members of the family Flaviviridae, to which HCV belongs, there have been few studies reporting recombination on natural populations of HCV. Recombination break-points have been identified in non structural proteins of the HCV genome. Given the implications that recombination has for RNA virus evolution, it is clearly important to determine the extent to which recombination plays a role in HCV evolution. In order to gain insight into these matters, we have performed a phylogenetic analysis of 89 full-length HCV strains from all types and sub-types, isolated all over the world, in order to detect possible recombination events. METHOD: Putative recombinant sequences were identified with the use of SimPlot program. Recombination events were confirmed by bootscaning, using putative recombinant sequence as a query. RESULTS: Two crossing over events were identified in the E1/E2 structural region of an intra-typic (1a/1c) recombinant strain. CONCLUSION: Only one of 89 full-length strains studied resulted to be a recombinant HCV strain, revealing that homologous recombination does not play an extensive roll in HCV evolution. Nevertheless, this mechanism can not be denied as a source for generating genetic diversity in natural populations of HCV, since a new intra-typic recombinant strain was found. Moreover, the recombination break-points were found in the structural region of the HCV genome.

Evolution, Molecular↗
PubMed2006

Phylogenetic mapping of recombination hotspots in human immunodeficiency virus via spatially smoothed change-point processes.

We present a Bayesian framework for inferring spatial preferences of recombination from multiple putative recombinant nucleotide sequences. Phylogenetic recombination detection has been an active area of research for the last 15 years. However, only recently attempts to summarize information from several instances of recombination have been made. We propose a hierarchical model that allows for simultaneous inference of recombination breakpoint locations and spatial variation in recombination frequency. The dual multiple change-point model for phylogenetic recombination detection resides at the lowest level of our hierarchy under the umbrella of a common prior on breakpoint locations. The hierarchical prior allows for information about spatial preferences of recombination to be shared among individual data sets. To overcome the sparseness of breakpoint data, dictated by the modest number of available recombinant sequences, we a priori impose a biologically relevant correlation structure on recombination location log odds via a Gaussian Markov random field hyperprior. To examine the capabilities of our model to recover spatial variation in recombination frequency, we simulate recombination from a predefined distribution of breakpoint locations. We then proceed with the analysis of 42 human immunodeficiency virus (HIV) intersubtype gag recombinants and identify a putative recombination hotspot.

Animals↗
PubMedDate not supplied

Mechanistic features of recombination in HIV.

The importance of recombination in retroviral evolution has been acknowledged for several decades. Consequently, after the identification of HIV as the etiological agent of AIDS, it was suspected that recombination could also play a central role in the evolution of this virus. However, only recently, extensive epidemiologic studies of HIV infections worldwide have provided an estimate for the occurrence of recombination in vivo, unveiling recombination frequencies that dwarf those initially expected. Nowadays, recombination is regarded as an integral part of the infectious cycle of this retrovirus, which impacts on diagnosis and treatment of infections, especially when genetically distant viruses have been at the origin of the recombinant forms. Retroviral recombination is observed when two genetically divergent genomic RNA molecules are present in the same viral particle, and arises during the reverse transcription step. This review focuses on the mechanisms that have been proposed to account for the occurrence of recombination in retroviruses, from the strand displacement model, according to which recombination occurs during second DNA strand synthesis; to the description of the factors responsible for copy-choice recombination during first DNA strand synthesis, such as the presence of breaks, pause sites, or secondary structures in the genomic RNA. Most of these models have been supported by experimental data obtained from in vitro reconstituted systems or from cell infection studies using academic model sequences. The situation in vivo is expected to be more complex, since several factors come into play when recombination involves relatively distant isolates, as in the case of inter-subtype recombination. At present, it is clear that further studies are needed in order to evaluate whether a prevailing mechanism exists for in vivo recombination, and these studies will also be essential for understanding how the underlying mechanisms of recombination contribute to the evolution of HIV.

Evolution, Molecular↗
PubMed2024

Evolution of homologous recombination rates across bacteria.

Bacteria are nonsexual organisms but are capable of exchanging DNA at diverse degrees through homologous recombination. Intriguingly, the rates of recombination vary immensely across lineages where some species have been described as purely clonal and others as "quasi-sexual." However, estimating recombination rates has proven a difficult endeavor and estimates often vary substantially across studies. It is unclear whether these variations reflect natural variations across populations or are due to differences in methodologies. Consequently, the impact of recombination on bacterial evolution has not been extensively evaluated and the evolution of recombination rate-as a trait-remains to be accurately described. Here, we developed an approach based on Approximate Bayesian Computation that integrates multiple signals of recombination to estimate recombination rates. We inferred the rate of recombination of 162 bacterial species and one archaeon and tested the robustness of our approach. Our results confirm that recombination rates vary drastically across bacteria; however, we found that recombination rate-as a trait-is conserved in several lineages but evolves rapidly in others. Although some traits are thought to be associated with recombination rate (e.g., GC-content), we found no clear association between genomic or phenotypic traits and recombination rate. Overall, our results provide an overview of recombination rate, its evolution, and its impact on bacterial evolution.

Bacteria↗
PubMed1998

Hox gene expression, AV-1 antigen expression, and cartilage pattern formation in chick recombinant limb buds.

A recombinant limb bud composed of dissociated and reaggregated mesenchyme and an ectodermal jacket develops a limblike structure with bifurcated and segmented cartilage. We compared the cartilage structure formed from recombinants that were composed of mesenchymal cells derived from the limb bud progress zone at various stages. In the case of recombinants containing distal mesenchyme of early-stage limb buds (stage 18 or 20), long and thick cartilage structures were formed in the proximal region, and segmented digitlike structures were formed in the distal region. On the contrary, in the case of recombinants containing distal mesenchyme of late-stage limb buds (stage 25 or 27), only poorly developed cartilage structures were formed. Next, we analyzed expression patterns of the position-specific genes HoxA11, A13 and D12 and the position-specific antigen AV-1 protein in recombinants containing distal mesenchyme of stage 20 limb buds (stage 20 recombinants) or stage 25 limb buds (stage 25 recombinants). In stage 20 recombinants, HoxA11 was expressed throughout the mesenchyme, but HoxA13 was expressed only in the distal half of the mesenchyme. In stage 25 recombinants, HoxA13 was expressed throughout the mesenchyme, but HoxA11 was only faintly expressed. The expression pattern of HoxD12 was similar to that of HoxA13 in both stage 20 and stage 25 recombinants, and no asymmetric expression pattern, which is observed in normal limb buds, was detected. AV-1 antigen was expressed in the core region of stage 20 recombinants, and anteroposterior asymmetry, which is observed in the anterior-ventral-distal region of normal limb buds, was not found. No AV-1 expression was observed in stage 25 recombinants. These results suggest that the mesenchyme in recombinants shows spatially controlled gene/protein expressions along the proximodistal axis, and that these differences in gene/protein expressions may affect cartilage pattern formation in recombinants.

Animals↗
PubMed2003

The N-terminal DNA-binding domain of Rad52 promotes RAD51-independent recombination in Saccharomyces cerevisiae.

In Saccharomyces cerevisiae, the Rad52 protein plays a role in both RAD51-dependent and RAD51-independent recombination pathways. We characterized a rad52 mutant, rad52-329, which lacks the C-terminal Rad51-interacting domain, and studied its role in RAD51-independent recombination. The rad52-329 mutant is completely defective in mating-type switching, but partially proficient in recombination between inverted repeats. We also analyzed the effect of the rad52-329 mutant on telomere recombination. Yeast cells lacking telomerase maintain telomere length by recombination. The rad52-329 mutant is deficient in RAD51-dependent telomere recombination, but is proficient in RAD51-independent telomere recombination. In addition, we examined the roles of other recombination genes in the telomere recombination. The RAD51-independent recombination in the rad52-329 mutant is promoted by a paralogue of Rad52, Rad59. All components of the Rad50-Mre11-Xrs2 complex are also important, but not essential, for RAD51-independent telomere recombination. Interestingly, RAD51 inhibits the RAD51-independent, RAD52-dependent telomere recombination. These findings indicate that Rad52 itself, and more precisely its N-terminal DNA-binding domain, promote an essential reaction in recombination in the absence of RAD51.

Cell Division↗