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Results for “recombination suppression”

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At least 37 records · Page 2Linked to original sources
PubMed1975

Indirect suppression of radiation sensitivity of a recA- strain of Escherichia coli K12.

It has been shown previously that the radiation sensitivity of LexA strains of Escherichia coli K-12 can be suppressed by thermosensitive mutations (designated tsl) that are closely linked to the lexA locus. These are thought to be intragenic suppressors that reduce the activity of the diffusible product that gives rise to the LexA- phenotype (Mount et al., 1973). When a recA mutation is crossed into a suppressed tsl- strain, the extreme radiation sensitivity usually conferred by a recA mutation is considerably reduced without any detectable change in genetic recombination deficiency. Suppression of UV sensitivity depends upon the activity of the uvrA+ product. We propose that at least part of the radiation sensitivity of a recA- strain is due to a DNA repair defect that is different from inability to perform genetic exchanges and depends upon the presence of the lexA+ product. We hypothesize that the lexA+ product is a repressor of the synthesis of repair enzymes. In recA+ cells with DNA lesions, repressor is inactivated leading to enzyme induction but this does not occur in recA- cells. tsl mutations inactivate repressor leading to constitute enzyme synthesis and bypassing the need for recA+ product to inactivate the lexA+ product.

Cell Survival↗
PubMed1975

A genetic analysis of phototactic behavior in Drosophila melanogaster. II. Hybridization of divergent populations.

Artificial selection has produced populations of Drosophila melanogaster which show either positive or negative phototactic behavior. Selection was carried out in the presence of various marked multiple inversions used to suppress genetic recombination. Reciprocal hybridizations between photopositive and photonegative populations of flies have revealed the X chromosome of D. melanogaster to be important in phototactic behavior regardless of conditions which restricted genetic recombination during selection.

Animals↗
PubMed2025

Heterologous expression and optimization of the antimicrobial peptide acidocin 4356 in Komagataella phaffii to target Pseudomonas aeruginosa.

Multidrug-resistant (MDR) pathogens, particularly Pseudomonas aeruginosa, pose a serious global health threat due to their increasing prevalence and limited therapeutic options. Antimicrobial peptides (AMPs) offer promising alternatives to traditional antibiotics, yet their large-scale application remains constrained by high production costs and technical challenges. This research sought to develop a yeast-based system for the cost-efficient synthesis of acidocin 4356 (ACD), an antimicrobial peptide proven effective against P. aeruginosa. A codon-optimized ACD gene was cloned into the pPICZα-A expression vector and integrated into the Komagataella phaffii (formerly Pichia pastoris) GS115 genome. Colony PCR confirmed successful integration, and specific transformants demonstrated expression of the 6 × His-ECS-rACD fusion protein, as verified by SDS-PAGE and dot blot analysis. After Ni-NTA chromatography and enterokinase digestion, rACD was found at ~ 20 kDa instead of 8.3 kDa, suggesting oligomerization or post-translational modifications. Response surface methodology determined the optimal temperature, pH, and methanol concentration for peptide synthesis. Under optimal circumstances (21 °C, pH 6.24, and 1.089% methanol), rACD synthesis increased by 34.12% over baseline conditions (30 °C, pH 6, 1% methanol). AlphaFold structural modeling identified three α-helices in high-confidence regions, implicated in bacterial membrane disruption. Antimicrobial assays demonstrated potent rACD activity against P. aeruginosa, yielding a 58.29% reduction in growth at 150 µg/mL and MIC50 and MIC90 values of 143.04 and 320.64 µg/mL, respectively. These findings underscore K. phaffii as a robust platform for AMP production and highlight rACD's therapeutic potential as an effective agent against MDR P. aeruginosa, warranting further investigation into its clinical and industrial applications. KEY POINTS: • Developing a novel K. phaffii strain for heterologous expression supports efficient rACD peptide production. • Optimized conditions boosted expression yield by 34.12% above the reference fermentation settings. • Recombinant acidocin suppressed Pseudomonas aeruginosa growth by 58%, indicating anti-MDR activity.

Pseudomonas aeruginosa↗
PubMed1978

Genetic method for the preferential elimination of females of anopheles albimanus.

Recent field experiments demonstrated the possibility of using the sterile male method for the control of Anopheles albimanus Wiedemann, the most important vector of human malaria in Central America. Until now there was no practical method for excluding females from the releases of sterile males. A genetic method was developed for the preferential elimination of females during any of the four life stages. This genetic sexing system utilizes propoxur (o-isopropoxyphenyl methyl-carbamate) susceptibility as a recessive conditional lethal a T(Y:2R) translocation, and an In(2R)inversion. The propoxur resistance allele (dominant) was linked to the Y chromosome via a radiation-induced translocation, and genetic recombination was suppressed by inversions. In one of the strains produced, 99.7 percent of the females are eliminated when treated with propoxur, without male loss.

Animals↗
PubMed1977

Formation of HfrH-type donor cells as a result of integrative suppression by R-F recombinant plasmids.

Three recombinant plasmids, resulting from recombination between an R plasmid of the FI incompatibility group and the F of HfrH, were introduced in a temperature-sensitive dnaA mutant to isolate Hfr-type-donors. All of the temperature-insensitive clones isolated from two of the three recombinant plasmids had the same origin and transfer pattern as the parental HfrH strain.

Chromosomes, Bacterial↗
PubMed1979

Suppression of the formation of polygenotypic recombinant colonies by a maf mutation in mating with HfrH.

W3011, a Cavalli-type Hfr (HfrC), was mated with F-KY9474, maf-1, which cannot maintain F or F-like plasmids, and with F-OU9474, Maf+, a spontaneous revertant of KY9474. The recombinant colonies obtained were 100% monogenotypic from KY9474 and 90% monogenotypic from OU9474. On the other hand, in matings with OU11, a Hayes-type Hfr (HfrH), and these two F- strains, recombinant colonies derived from KY9474 showed only 22% polygenotypic recombinant colonies; whereas, those derived from OU9474 showed a high production rate (57%) of polygenotypic recombinant colonies. Among the polygenotypic recombinant colonies derived from KY9474 maf-1, 50% contained three or more recombinant types. These were probably derived from a small fraction of Maf+ revertants in the KY9474 population, as suggested by the results of mating this strain with M80, an F' strain that contains an amber mutation in traH. These results support the hypothesis that the donor DNA fragments derived from an HfrH can undergo a limited replication in the recipient to produce polygenotypic recombinant colonies, whereas those derived from HfrC cannot.

Escherichia coli↗
PubMed1977

Involvement of DNA-dependent RNA polymerase in a recA-independent pathway of genetic recombination in Escheria coli.

Recombinant DNA molecule of phage lambda formed in Escherichia coli in the presence of chloramphenicol and/or rifampin can be assayed by their biological activity. recA- cells were found to be capable of forming recombinant lambda phage DNA in the presence of chloramphenicol. The relatively high recA-independent recombination observed in this system contrasts with the relatively low recA-independent recombination when recombinant phage particles rather than recombinant DNA are titrated. Formation of the recombinant DNA was suppressed by the the addition of rifampin. The introduction of the rif-r mutation into host bacteria made their recombination activity rifampin-resistant. These results show that DNA-dependent RNA polymerase (EC 2.7.7.6) is involved in this recA-independent pathway of recombination, which is named the "Rpo pathway." This is distinct from Red, Int, RecBC, RecE, or Der pathways of recombination. Crossover was much more frequent in the N-PL-cI and cI-PR-O regions than in the A-D and O-S regions. The crossover seems to occur in the regions that are transcribed actively. Some local change of DNA structure caused by transcription might be required for the Rpo pathway of recombination.

Coliphages↗
PubMed1977

A search for allelic recombination in Chinese hamster cell hybrids.

Mutants resistant to 6-thioguanine were selected from CHO cells which were either temperature sensitive or proline requiring. These mutants were stable and had low levels of hypoxanthine guanine phosphoribosyl transferase (HGPRT). Hybrids were selected which were heteroallelic at the hgprt locus and complementation between the mutants used was not observed. Interallelic recombination at this locus would generate hgprt+ cells which could be selected in Littlefield's HAT medium. Selection experiments with hybrids containing three different pairs of mutants yielded no recombinants among populations of 4 x 106 - 2 x 107 cells. After treatment with the recombinagen mitomycin C, 3 putative recombinants were detected amongst 1.4 x 107 surviving cells from one hybrid. One of these strains was examined and shown to have a normal level of HGPRT and its heterozygosity at this locus was demonstrated by the segregation of colonies resistant to 6-thioguanine. It cannot be excluded that the rare hgprt+ colonies seen arose by mutation rather than by recombination. Mitotic allelic recombination therefore appears to be a much less frequent event in CHO cells than it is in lower eukaryotes. It is possible that mitotic recombination is effectively suppressed in mammalian cells to prevent the expression of deleterious recessive mutants.

Alleles↗
PubMed2025

BET family BRD3 initiates DSB-induced chromatin remodeling with TIP60 to promote R-loop-mediated HR.

Mechanisms for genome stability in actively transcribed regions are essential for cellular homeostasis; however, these mechanisms are poorly understood. Herein, we identify the bromodomain and extraterminal domain (BET) family BRD3 as the genome caretaker in actively transcribed chromatin. We identify the protein network between BRD3 and chromatin remodeler TIP60. During transcription, BRD3 localizes to actively transcribed chromatin through its N-terminal bromodomains. Following DNA double-strand breaks (DSBs) at the actively transcribed chromatin, the C-terminal extraterminal (ET) domain of BRD3 recruits CHD4 via its KIKL-like motifs to replace HP1 with the TIP60 (Tat-interactive protein, 60 kDa) complex, promoting H4K16 acetylation and MBTD1 recruitment, which creates chromatin barriers to 53BP1. This process recruits BRCA1 and R-loop-processing factors to promote R-loop-mediated homologous recombination (HR) and suppress 53BP1 and mutagenic non-homologous end-joining. Our study elucidates the mechanism by which BRD3 initiates DSB-induced chromatin remodeling by CHD4 and TIP60 to promote R-loop-mediated HR on actively transcribed chromatin to maintain genome stability.

Humans↗
PubMed1975

Heterochromatin and multiple inversions in a Drosophila chromosome.

A chromosomal polymorphism is described from a Maui (Hawaii) population of D. disjuncta. The acquisition of an extra heterochromatic segment in a mitotic chromosome is specifically associated with the presence of multiple inversions in the same chromosome. This suggests the possible effect of a chromosomal break-point within the area of centromeric heterochromatin in causing an increase in the amount of repetitive DNA. The possibility exists that the extra heterochromatin may play a role in the suppression of gene recombination in a certain region of the chromosome and/or in strengthening pairing of the inversion-laden chromosome with its normal homologue. This may reduce the changes of sterility due to nondisjunction during meiosis.

Animals↗
PubMed1975

Genetic evidence for an additional function of phage T4 gene 32 protein: interaction with ligase.

Gene 32 of bacteriophage T4 is essential for DNA replication, recombination, and repair. In an attempt to clarify the role of the corresponding gene product, we have looked for mutations that specifically inactivate one but not all of its functions and for compensating suppressor mutations in other genes. Here we describe a gene 32 ts mutant that does not produce progeny, but in contrast to an am mutant investigated by others, is capable of some primary and secondary DNA replication and of forming "joint" recombinational intermediates after infection of Escherichia coli B at the restrictive temperature. However, parental and progeny DNA strands are not ligated to covalently linked "recombinant" molecules, and single strands of vegetative DNA do not exceed unit length. Progeny production as well as capacity for covalent linkage in this gene 32 ts mutant are partially restored by additional rII mutations. Suppression by rII depends on functioning host ligase [EC 6.5.1.2; poly(deoxyribonucleotide):poly(deoxyribonucleotide) ligase (AMP-forming, NMN-forming)]. This gene 32 ts mutation (unlike some others) in turn suppresses the characteristic plaque morphology of rII mutants. We conclude that gene 32 protein, in addition to its role in DNA replication and in the formation of "joint" recombinational intermediates, interacts with T4 ligase [EC 6.5.1.1; poly(deoxyribonucleotide):poly(deoxyribonucleotide) ligase (AMP-forming)] when recombining DNA strands are covalently linked. The protein of the mutant that we describe here is mainly defective in this interaction, thus inactivating T4 ligase in recombination. Suppressing rII mutations facilitate substitution of host ligase. There is suggestive evidence that these interactions occur at the membrane.

Binding Sites↗
PubMed1976

Mitochondrial DNA in yeast recombination and subsequent modification following mating between a Grande and a suppressive Petite.

The fate of mitochondrial DNA, following mating between a grande and suppressive petite of Saccharomyces cerevisiae, has been followed for up to 60 generations. The buoyant density of the mitochondrial DNA was seen to change in a manner explicable by a combination of recombination and subsequent modification phenomena whilst the suppressivity of the petite zygotic clones always remained high. These findings are consistent with current models of mitochondrial DNA metabolism in which petite strains have been observed to undergo deletion and reamplification of certain parts of their genomes.

Centrifugation, Density Gradient↗
PubMed1978

Suppressibility of recA, recB, and recC mutations by nonsense suppressors.

Mutations in the recA, recB, and recC genes of Escherichia coli K-12 were surveyed to ascertain whether or not they are suppressed by nonsense suppressors. Several mutations which map in or near the recA gene, but have not been called recA mutations, were also surveyed. An amber recB mutation, recB156, and an amber recC mutation, recC155, were isolated. One recB mutation, recB95, and four recC mutations, recC22, recC38, recC82, and recC83, were found to be suppressed by a UGA suppressor. In addition to the previously isolated amber recA mutation recA99, two other recA mutations, recA52 and recA123, were found to be suppressed by amber suppressor supD32 but not by supE44.

Escherichia coli↗
PubMed1975

[Mechanism of conjugation in Escherichia coli K-12. IV. Conjugation in conditions of phenotypic suppression of gene dnaB mutation].

The thermosensitive mutation BT43 in the gene dnaB is a missence mutation affecting the vegetative and conjugational DNA synthesis. By means of the increase of ionic strength (NaCl concentration) in the medium the functional activity of the dnaB product is partially restored in non-permissive conditions. In these conditions a rescue of recombinant yield is observed. But the mechanism of recombination is switched from one-stranded to double-stranded. This is demonstrated by the alteration of the degree of linkage of genetically close markers.

DNA, Bacterial↗
PubMed1976

[Suppression of DNA-ligase deficiency and selective breeding of mutants and recombinants of T4 phage with phenotype rII].

A number of methods which greatly simplify the introduction of frame shift mutations in the limited segment of the phage T4 rII genes were developed for studying genetical recombination between closely linked markers. These methods enable to construct multiple rII mutants with relatively small expenditure of labour. Suppression of gene 30 deficiency by rII mutations has been studied for a variety of conditions. The results obtained indicate that rIIB polypeptide is involved in two different activities: rIIB region which is dispensable for growth on lambda-lysogenic Escherichia coli strains behaves as indispensable in phenomenon of suppression of ligase deficiency.

Coliphages↗
PubMed1977

Simple Mendelian inheritance of the reiterated ribosomal DNA of yeast.

A diploid strain of yeast (Saccharomyces cerevisiae) was found to be heterozygous for two forms of the highly repetitious ribosomal DNA. These forms could be distinguished by the pattern of fragments produced after digestion with the site-specific restriction endonuclease EcoRI. The mode of inheritance of ribosomal DNA was determined by tetrad analysis. Of 14 tetrads analyzed, 12 clearly showed the ribosomal DNA forms segregating as a single Mendelian unit. The simplest interpretation of this result is that all of the approximately 100 copies of the ribosomal DNA genes of the yeast cell are located on one chromosome and that meiotic recombination within these genes is suppressed. Two of the 14 tetrads showed the segregation patterns expected as the result of mitotic recombination within the ribosomal DNA.

Base Sequence↗