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At least 361 records · Page 20Linked to original sources
PubMed2006

The few virus-like genes of Cotesia congregata bracovirus.

The origin of the symbiotic association between parasitoid wasps and bracoviruses is still unknown. From phylogenetic analyses, bracovirus-associated wasp species constitute a monophyletic group, the microgastroid complex. Thus all wasp-bracovirus associations could have originated from the integration of an ancestral virus in the genome of the ancestor of the microgastroids. In an effort to identify a set of virus genes that would give clues on the nature of the ancestral virus, we have recently performed the complete sequencing of the genome of CcBV, the bracovirus of the wasp Cotesia congregata. We describe here the putative proteins encoded by CcBV genome having significant similarities with sequences from known viruses and mobile elements. The analysis of CcBV gene content does not lend support to the hypothesis that bracoviruses originated from a baculovirus. Moreover, no consistent homology was found between CcBV genes and any set of genes constituting the core genome of a known free-living virus. We discuss the significance of the scarce homology found between proteins from CcBV and other viruses or mobile elements.

Amino Acid Sequence↗
PubMed1988

Second-element turn-on of gene expression in an IS1 insertion mutant.

To learn more about the ways in which genes silenced by insertion mutations can be reactivated, we have undertaken a systematic investigation of Gal+ revertants of the polar mutant galOP-306::IS1 in Escherichia coli K12. The selective conditions used excluded reversion to wild type by precise excision of IS1. In this system (which resided on a multi-copy plasmid) reversion to the Gal+ phenotype occurred with a frequency of about 10(-7) per cell and per generation. Analysis of the revertants revealed that - with the single exception of the previously published chromosomal mutant sis1 - alterations in the structure of IS1 lead to reactivation of gal operon expression. These events fall into four classes: (I) insertion of IS2 at position 327 in IS1, insertion of IS2 at position 687 in IS1, (III) insertion of a hitherto undetected mobile element, IS150, at position 387, (IV) a 16-bp deletion encompassing IS1 coordinates 553-568. Of some 200 independent reversion events studied, all but one were of types I-III i.e. they involved the intervention of a second mobile element.

Base Sequence↗
PubMed2006

Occurrence, prevalence and genetic environment of CTX-M beta-lactamases in Enterobacteriaceae from Indian hospitals.

OBJECTIVES: To determine occurrence, prevalence and CTX-M genotypes produced by Enterobacteriaceae from clinical samples from three geographically distant Indian hospitals and to detect linkage of IS26 with bla(CTX-M) and map its precise insertion position. METHODS: A total of 130, non-duplicate Escherichia coli and Klebsiella pneumoniae resistant to a third-generation cephalosporin (3GC) from three Indian centres were screened for extended-spectrum beta-lactamase (ESBL) production using phenotypic detection methods. All isolates were screened for bla(CTX-M) using multiplex PCR. Precise CTX-M genotype was identified using reverse-line hybridization. All CTX-M-producing isolates were screened for linkage of IS26 with bla(CTX-M). DNA sequencing was used to map the exact insertion position of this mobile element. RESULTS: Ninety-five of 130 3GC-resistant (73%) (73% of total E. coli, 72% of total K. pneumoniae) isolates were found to carry bla(CTX-M-15). No other CTX-M genotype was detected. IS26 linkage with bla(CTX-M-15) was detected in 31% of isolates carrying bla(CTX-M-15). DNA sequencing revealed variable insertion of this mobile element within tnpA of ISEcp1. RAPD-PCR typing demonstrated great diversity in isolates carrying bla(CTX-M-15); no predominant clone was identified. CONCLUSIONS: In contrast with other studies where greater diversity exists, CTX-M-15 was the only CTX-M ESBL produced in this Indian collection of unrelated E. coli and K. pneumoniae. This is the first systematic survey report from India detecting CTX-M-type beta-lactamases This is also the first report indicating such high mobility/diversity of insertion of IS26 in close association with bla(CTX-M) in a single bacterial collection.

Anti-Bacterial Agents↗
PubMed2001

Involvement of sigma(S) in starvation-induced transposition of Pseudomonas putida transposon Tn4652.

Transpositional activity of mobile elements can be induced by different environmental stresses. Here, we present evidence that transposition of Tn4652 is elevated in stationary-phase Pseudomonas putida and suppressed in an isogenic sigma(S)-defective strain. We demonstrate that transcription from the Tn4652 transposase promoter is controlled by the stationary-phase-specific sigma factor sigma(S). To our knowledge, this is the first example of direct stationary-phase-specific regulation of a mobile element transposase. Data presented in this report support the idea that activation of transposition under stressful conditions could be an inducible process.

Bacterial Proteins↗
PubMed1987

The relationship between radiation-induced and transposon-induced genetic damage during Drosophila spermatogenesis.

The combined effect of transposon mobility and X-rays on X-linked recessive lethals and dominant lethals was measured in the germ line of F1 male hybrids in the P-M system of hybrid dysgenesis. X-Linked lethal mutation rate was measured in the chromosome derived from the P-strain father of the M X P cross. Mutations induced in irradiated dysgenic males were compared to those of unirradiated males, as well as to irradiated nondysgenic males derived from M X M crosses. Three four-day broods of sperm were tested for both X-linked lethals and dominant lethals. X-Linked lethal mutation rate in dysgenic control males was 6.38%, 6.36% and 4.55% in broods 1, 2 and 3 respectively, thus showing a decrease in older males. The mutation rate in the same broods of irradiated, nondysgenic control males was 3.66%, 4.46% and 6.38%, respectively. The rate obtained in dysgenic irradiated males was 10.33, 11.16 and 7.97 in the same 3 broods. These results demonstrate that when X-rays and P element mobility were combined as a source of mutagenesis, a strictly additive effect on genetic damage was observed in the first two broods of sperm which represent primarily mature sperm and spermatids respectively. The third brood, representing mostly spermatocytes showed a less than additive effect, probably due to germinal selection. In contrast, the induction of dominant lethals showed a clearly synergistic effect in the last two broods of sperm tested, when X-rays and transposon mobility were combined. The X-ray component of dominant lethality in brood 1, representing mostly mature spermatozoa, was negative, indicating a lower than expected lethality induced by X-irradiation in the presence of P element mobility. The X-ray-induced component of dominant lethality, was expressed as the per cent of embryo lethality after adjusting the results obtained with each brood of sperm from nondysgenic and dysgenic males to their respective unirradiated controls. These values were 32.3%, 30.5% and 64.7% for brood 1, 2 and 3 respectively from nondysgenic males, and 14.1%, 56.1% and 71.4% for the same broods from dysgenic males. Thus the differential effect of X-rays in sperm broods 1, 2 and 3 was -18.2, +25.6 and +6.7% respectively. These results suggest that the synergistic effect may be due to the common component of X-ray and P element-induced genetic damage, namely chromosome breaks, and that the interaction of these lesions resulted in a greater than additive number of of unrestituted chromosome breaks and nonviable chromosomal rearrangements.

Animals↗
PubMed1998

Evaluation of resilient abutment components on measured strain using dynamic loading conditions.

STATEMENT OF PROBLEM: Factors that affect transmission of strain from prostheses to bone may affect the long-term success of loaded implants. Current in vitro models are theoretically predictive (finite element modeling) or facsimile (photoelastic) in nature. A more clinically relevant in vitro model for strain evaluation should be investigated. PURPOSE: This study attempted: (1) to validate a human cadaver bone model for vitro measurement of cortical bone strain, and (2) to evaluate the effect on cortical strain measurements of a resilient plastic component incorporated within a titanium implant in response to variable dynamic loading. MATERIAL AND METHODS: Two IMZ (Interpore International) abutment alternatives were used: the titanium Abutment Complete and the polyoxymethylene Intra-mobile Element. The model system consisted of two implants placed in unfixed human cadaver ulna bone to simulate an implant bound edentulous region. Four biaxial rosette strain gauges simultaneously recorded cortical bone strain immediately mesial and distal to each implant. During experimentation a simulated prosthetic framework supported by either titanium or polyoxymethylene abutments was dynamically loaded 6 min from the terminal abutment along a cantilever extension. Cyclic nominal peak loads were applied with a materials testing machine at 20-N intervals from 20 to 200 N at a crosshead speed of 5 mm/minute. The protocol allowed frequency of load application to vary. A Newtonian linear correlation (r2 > or = 0.98) between load application and strain output was determined for each gauge position except for the terminal gauge located opposite the cantilever. RESULTS: Cortical strains recorded were within reported physiologic ranges involved in bone modeling and remodeling. Further, the polyoxymethylene abutment components did not result in reduction of peak microstrain at any gauge position. The Intra-mobile Element abutments, however, did increase the time required to complete 10 loading cycles when compared with the titanium Abutment Complete abutments for the crosshead speed and ultimate loads evaluated. CONCLUSIONS: Results indicate the cadaver bone behaved in an elastic manner within the load range evaluated, and as such represents a viable in vitro experimental model. Under these conditions, polyoxymethylene abutment components do not affect measurable bone strain in response to variable loading when compared with titanium.

Bone and Bones↗
PubMed2004

Jittery, a Mutator distant relative with a paradoxical mobile behavior: excision without reinsertion.

The unstable mutation bz-m039 arose in a maize (Zea mays) stock that originated from a plant infected with barley stripe mosaic virus. The instability of the mutation is caused by a 3.9-kb mobile element that has been named Jittery (Jit). Jit has terminal inverted repeats (TIRs) of 181 bp, causes a 9-bp direct duplication of the target site, and appears to excise autonomously. It is predicted to encode a single 709-amino acid protein, JITA, which is distantly related to the MURA transposase protein of the Mutator system but is more closely related to the MURA protein of Mutator-like elements (MULEs) from Arabidopsis thaliana and rice (Oryza sativa). Like MULEs, Jit resembles Mutator in the length of the element's TIRs, the size of the target site duplication, and in the makeup of its transposase but differs from the autonomous element Mutator-Don Robertson in that it encodes a single protein. Jit also differs from Mutator elements in the high frequency with which it excises to produce germinal revertants and in its copy number in the maize genome: Jit-like TIRs are present at low copy number in all maize lines and teosinte accessions examined, and JITA sequences occur in only a few maize inbreds. However, Jit cannot be considered a bona fide transposon in its present host line because it does not leave footprints upon excision and does not reinsert in the genome. These unusual mobile element properties are discussed in light of the structure and gene organization of Jit and related elements.

Amino Acid Sequence↗
PubMed1995

Mobile gene cassettes and integrons: capture and spread of genes by site-specific recombination.

An integron is a genetic unit that includes the determinants of the components of a site-specific recombination system capable of capturing and mobilizing genes that are contained in mobile elements called gene cassettes. An integron also provides a promoter for expression of the cassette genes, and integrons thus act both as natural cloning systems and as expression vectors. The essential components of an integron are an int gene encoding a site-specific recombinase belonging to the integrase family, an adjacent site, attI, that is recognized by the integrase and is the receptor site for the cassettes, and a promoter suitably oriented for expression of the cassette-encoded genes. The cassettes are mobile elements that include a gene (most commonly an antibiotic-resistance gene) and an integrase-specific recombination site that is a member of a family of sites known as 59-base elements. Cassettes can exist either free in a circularized form or integrated at the attI site, and only when integrated is a cassette formally part of an integron. A single site-specific recombination event involving the integron-associated attI site and a cassette-associated 59-base element leads to insertion of a free circular cassette into a recipient integron. Multiple cassette insertions can occur, and integrons containing several cassettes have been found in the wild. The integrase also catalyses excisive recombination events that can lead to loss of cassettes from an itegron and generate free circular cassettes. Due to their ability to acquire new genes, integrons have a clear role in the evolution of the genomes of the plasmids and transposons that contain them.

Aspergillosis↗
PubMed1995

[Features of ontogenetic development of Drosophila melanogaster in the dysgenetic cross system].

Three families of mobile elements that induce P-M, H-E, and I-R hybrid dysgenesis in Drosophila melanogaster were activated by crossing files of different cytotypes. Manifestation of gonadal sterility in F1 hybrid progeny was dependent on the temperature of development. The systems differed significantly in lethality of F2 hybrids at various stages of ontogeny (embryos, larvae, pupae, and adult flies). The highest embryo lethality was found in the P-M system at the cleavage stage. In the I-R and H-E systems, the peak of embryonic death corresponded to the stages of blastoderm and organogenesis, respectively. Experimental results are discussed in view of molecular and cytological characteristics of interacting strains and existing hypotheses for regulation xof transposition of P, hobo, and I mobile elements.

Animals↗
PubMed2005

Nickel stimulates L1 retrotransposition by a post-transcriptional mechanism.

Sequence studies of the human genome demonstrate that almost half of the DNA is derived from mobile elements. Most of the current retrotransposition activity arises from L1 and the L1-dependent, non-autonomous elements, such as Alu, contributing to a significant amount of genetic mutation and genomic instability. We present data demonstrating that nickel chloride, but not cobalt chloride, is able to stimulate L1 retrotransposition about 2.5-fold. Our data suggest that the stimulation occurs at a post-transcriptional level, possibly during the integration process. The effect of nickel on the cell is highly complex, limiting the determination of the exact mechanism of this stimulation. The observed stimulation of L1 retrotransposition is not due to a general increase in L1 transcription or an increase in the number of genomic nicks caused by nickel, but more likely caused by a decrease in DNA repair activities that influence the downstream events of retrotransposition. Our observations demonstrate the influence of environmental toxicants on human retroelement activity. We present an additional mechanism for heavy-metal carcinogenesis, where DNA damage through mobile element activation must be considered when dealing with genomic damage/instability in response to environmental agents.

Cell Cycle↗
PubMed2007

Inferring a population structure for Staphylococcus epidermidis from multilocus sequence typing data.

Despite its importance as a human pathogen, information on population structure and global epidemiology of Staphylococcus epidermidis is scarce and the relative importance of the mechanisms contributing to clonal diversification is unknown. In this study, we addressed these issues by analyzing a representative collection of S. epidermidis isolates from diverse geographic and clinical origins using multilocus sequence typing (MLST). Additionally, we characterized the mobile element (SCCmec) carrying the genetic determinant of methicillin resistance. The 217 S. epidermidis isolates from our collection were split by MLST into 74 types, suggesting a high level of genetic diversity. Analysis of MLST data using the eBURST algorithm revealed the existence of nine epidemic clonal lineages that were disseminated worldwide. One single clonal lineage (clonal complex 2) comprised 74% of the isolates, whereas the remaining isolates were clustered into 8 minor clonal lineages and 13 singletons. According to our evolutionary model, SCCmec was acquired at least 56 times by S. epidermidis. Although geographic dissemination of S. epidermidis strains and the value of the index of association between the alleles, 0.2898 (P < 0.05), support the clonality of S. epidermidis species, examination of the sequence changes at MLST loci during clonal diversification showed that recombination gives rise to new alleles approximately twice as frequently as point mutations. We suggest that S. epidermidis has a population with an epidemic structure, in which nine clones have emerged upon a recombining background and evolved quickly through frequent transfer of genetic mobile elements, including SCCmec.

Algorithms↗
PubMed2003

Acquired tetracycline and/or macrolide-lincosamides-streptogramin resistance in anaerobes.

In general bacterial antibiotic resistance is acquired on mobile elements such as plasmids, transposons and/or conjugative transposons. This is also true for many antibiotic resistant anaerobic species described in the literature. Of the 23 different tetracycline resistant efflux genes identified, tet(B), tet(K), tet(L), and tetA(P) have been found in anaerobic species and six of the ten tetracycline resistant genes coding for ribosomal protection proteins, tet(M), tet(O), tetB(P), tet(Q), tet(W), and tet(32), have been identified in anaerobes. There are now three enzymes which inactivate tetracycline, of which the tet(X) has been identified in Bacteroides though is not functional under anaerobic growth conditions. A similar situation exists with the genes conferring macrolide-lincosamide-streptogramin (MLS) resistance. Of the 26 rRNA methylase MLS resistant genes characterized, five genes; erm(B), erm(C), erm(F), erm(G), and erm(Q), have been identified in anaerobes. In contrast, no genes coding for MLS resistant efflux proteins or inactivating enzymes have been described in anaerobic species. This mini-review will summarize what is known about tetracycline and MLS resistance in genera with anaerobic species and the mobile elements associated with acquired tetracycline and/or MLS resistance genes.

Journal Article↗
PubMed2006

DNA damage and L1 retrotransposition.

Barbara McClintock was the first to suggest that transposons are a source of genome instability and that genotoxic stress assisted in their mobilization. The generation of double-stranded DNA breaks (DSBs) is a severe form of genotoxic stress that threatens the integrity of the genome, activates cell cycle checkpoints, and, in some cases, causes cell death. Applying McClintock's stress hypothesis to humans, are L1 retrotransposons, the most active autonomous mobile elements in the modern day human genome, mobilized by DSBs? Here, evidence that transposable elements, particularly retrotransposons, are mobilized by genotoxic stress is reviewed. In the setting of DSB formation, L1 mobility may be affected by changes in the substrate for L1 integration, the DNA repair machinery, or the L1 element itself. The review concludes with a discussion of the potential consequences of L1 mobilization in the setting of genotoxic stress.

Journal Article↗
PubMed1997

P element domestication: a stationary truncated P element may encode a 66-kDa repressor-like protein in the Drosophila montium species subgroup.

Functional P transposable elements can be separated into two distinct classes: mobile elements, which present the canonical structure, with transposase and repressor functions, and immobile P sequences truncated in 5' and 3' by loss of the terminal inverted repeats and exon 3, which retain only the repressor function. This second class was first described in some species of the Drosophila obscura group. Here, we describe a new truncated immobile P sequence cloned from one species of the Drosophila montium subgroup (D. tsacasi) that produces a polyadenylated RNA with a coding capacity for a 66-kDa "repressor-like" protein. The results from a number of different comparisons between P-homologous sequences concerning both coding and noncoding regions strongly suggest that the obscura and montium immobile P sequences as well as the T-type P subfamily derive from the same ancestral mobile P element family. Study of the flanking regions of these immobile P sequences shows that the two immobilizations were produced by two independent events. Our results provide evidence that the molecular domestication of a transposable element family may recur in a species lineage.

Amino Acid Sequence↗
PubMed1995

Mobile genetic elements of Fusobacterium nucleatum.

The gram-negative anaerobic bacterium, Fusobacterium nucleatum, is a predominant member of the human oral flora. As a major component of subgingival plaque, this bacterium has a significant impact on the ecology of the oral cavity due to its ability to adhere to many different microbial species. The objective of this study was to identify and characterize plasmids and transposons that may have the potential to be developed into tools for cloning, genetic transformation, and mutagenesis of oral isolates of F. nucleatum. Analysis of a collection of laboratory strains resulted in the identification of a homologous family of small cryptic plasmids. Plasmids within this family ranged in size from 6.0 to 6.6 kb. Eighteen percent of all strains examined (n = 74) contained DNA sequences related to the plasmids. Homologous plasmid sequences were found in strains belonging to 2 of the 3 subspecies of the bacterium. The 2 smallest plasmid species were cloned in Escherichia coli to facilitate endonuclease restriction mapping. Among the strains examined for plasmids, 5 exhibited resistance to at least 10 micrograms/ml of tetracycline. These strains, all members of the subsp. polymorphum, contained a tetracycline resistance determinant (TetM) as part of a Tn916-like integrated transposon sequence. The Tn916-like element and 1 of the plasmid species co-resided in a single strain of the bacterium. Hybridization patterns of the Tn916-like sequences were identical in all 5 tetracycline-resistant strains. However, these strains appeared to be clonally distinct based on genomic fingerprinting.

Base Sequence↗
PubMed1992

Super-unstable mutations associated with P-M hybrid dysgenesis in Drosophila melanogaster.

Super-unstable mutations occasionally appear either in natural populations of Drosophila melanogaster or in P-M hybrid dysgenesis. We found that they may be reproducibly obtained with a high frequency from crosses between males from the pi 2 strain and females from the waG* strain or its derivatives. Super-unstable mutations in the ocelliless, singed, white, yellow and other loci have been obtained. Each super-unstable mutation gives rise to a large family of new super-unstable mutations with a wide range of phenotypic expression. Mutations with the same phenotype often differ in the specificity of their potential for further mutation. As a rule, a super-unstable mutation is associated with a specific reversible mutation and paired alleles are formed in this way. Other mutations are usually irreversible, but new mutations of these may also form paired alleles. Active transposase encoded by transposable P elements is necessary to maintain super-instability. Finally, some preliminary molecular data are discussed which suggest that this type of super-instability is a result of interaction between P elements and a novel mobile element, designated as X.

ATP-Binding Cassette Transporters↗