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At least 1,063 records · Page 59Linked to original sources
PubMed1994

Epigenetic regulation of the maize Spm transposable element: novel activation of a methylated promoter by TnpA.

Spm is epigenetically inactivated by C-methylation near its transcription start site. We have investigated the interaction between TnpA, an autoregulatory protein that can reactivate a silent Spm, and the promoter of the element. The promoter undergoes rapid de novo methylation and inactivation in stably transformed plants, but only if it includes a GC-rich sequence down-stream of the promoter. TnpA activates the inactive, methylated promoter and leads to reduced methylation. By contrast, TnpA represses the active, unmethylated Spm promoter. Only the internal DNA-binding and dimerization domains of the protein are required for repression, while activation requires an additional C-terminal sequence. TnpA is therefore a unique regulatory protein with a conventional transcriptional repressor activity and a novel ability to activate a methylated, inactive promoter.

Base Sequence↗
PubMed1993

Molecular characterization of an aberrant mercury resistance transposable element from an environmental Acinetobacter strain.

We present the complete nucleotide sequence of a mer operon located on a 60-kb conjugative plasmid pKLH2 from an environmental bacterium, Acinetobacter calcoaceticus, isolated from a mercury mine. The pKLH2 mer operon has essentially the same gene organization as that of Tn21 and Tn501 from clinical bacteria. The pKLH2 mer operon nucleotide sequence shows 85.5% identity with the Tn501 and 80.9% identity with the Tn21 sequences. Vestigial sequences have been found at the ends of the pKLH2 mer operon, indicating that the pKLH2 mer operon was once a part of a Tn21-like transposon, which had committed suicide by an aberrant resolution event.

Acinetobacter↗
PubMed2005

Differential excision patterns of the En-transposable element at the A2 locus in maize relate to the insertion site.

Defined mutant alleles with resident transposons display characteristic patterns of germinal and somatic reversion, and heritable changes in the timing and frequency of reversions, which have been termed "change of state" by McClintock, constantly arise. Several mechanisms were proposed to account for these changes. They may be ascribed to the structure and composition of the elements themselves (composition hypothesis) or to their location (position hypothesis). In the current study, insertion positions were determined for three autonomous En-controlled mutable alleles of the A2 locus in maize that show different somatic reversion patterns. A relationship was observed between En insertion positions in the single coding region of the intronless A2 gene and anthocyanin variegation patterns in the aleurone. An insertion in the 5' region of the coding sequence produced a very late somatic variegation pattern, whereas two early variegation patterns were caused by En insertions in the 3' region of the coding sequence.

Alleles↗
PubMed2002

Suppressors of transcriptional transgenic silencing in Chlamydomonas are sensitive to DNA-damaging agents and reactivate transposable elements.

In the unicellular green alga Chlamydomonas reinhardtii, the epigenetic silencing of transgenes occurs, as in land plants, at both the transcriptional and posttranscriptional levels. In the case of single-copy transgenes, transcriptional silencing takes place without detectable cytosine methylation of the introduced DNA. We have isolated two mutant strains, Mut-9 and Mut-11, that reactivate expression of a transcriptionally silenced single-copy transgene. These suppressors are deficient in the repression of a DNA transposon and a retrotransposon-like element. In addition, the mutants show enhanced sensitivity to DNA-damaging agents, particularly radiomimetic chemicals inducing DNA double-strand breaks. All of these phenotypes are much more prominent in a double mutant strain. These observations suggest that multiple partly redundant epigenetic mechanisms are involved in the repression of transgenes and transposons in eukaryotes, presumably as components of a system that evolved to preserve genomic stability. Our results also raise the possibility of mechanistic connections between epigenetic transcriptional silencing and DNA double-strand break repair.

Animals↗
PubMed1988

The structure of the regulatory region of the rat L1 (L1Rn, long interspersed repeated) DNA family of transposable elements.

Here we report the DNA structure of the left 1.5 kb of two newly isolated full length members of the rat L1 DNA family (L1Rn, long interspersed repeated DNA). In contrast to earlier isolated rat L1 members, both of these contain promoter-like regions that are most likely full length. In addition, the promoter-like region of both members has undergone a partial tandem duplication. A second internal region of the left end of one of the reported members is also tandemly duplicated. The propensity of the left end of rat L1 elements to undergo this form of genetic rearrangement, as well as other structural features revealed by the present work, is discussed in light of the fact that during evolution the otherwise conserved mammalian L1 DNA families have each acquired completely different promoter-like regions. In an accompanying paper [Nur, I., Pascale, E., and Furano, A. V. (1988) Nucleic Acids Res. 16, submitted], we report that one of the rat promoter-like regions can function as a promoter in rat cells when fused to the Escherichia coli chloramphenicol acyltransferase gene.

Amino Acid Sequence↗
PubMed1990

Mitomycin C induces genomic rearrangements involving transposable elements in Drosophila melanogaster.

Mitomycin C was injected into the abdomen of male flies of the y2 sc1 waG strain of Drosophila melanogaster. They were mated with females bearing attached-X chromosomes, and the male offspring (F1) were analysed for the appearance of mutations in the X chromosome. We observed y+ and sc+ reversions induced either by excision of mdg4 (gypsy) with retention of one long terminal repeat (LTR) or by insertion of a foreign sequence into mdg4, partial reversion of the waG mutation, waG----waGd, and unstable f mutations. The overall mutation frequency was considerably higher than in control flies of the y2 sc1 waG strain. Possible mechanisms of genomic rearrangements induced by Mitomycin C, in particular the role of homologous recombination, are discussed.

Animals↗
PubMed2006

Genetic association of blaSHV-5 with transposable elements IS26 and IS5 in Klebsiella pneumoniae from Taiwan.

A cloned 5,248-bp EcoRI fragment from the Klebsiella pneumoniae transferable plasmid pKP53 (> 70 kb) containing bla(SHV-5) was sequenced. Insertion sequences IS26 and IS5 were found downstream from bla(SHV-5). The DNA sequences of the genetic environment surrounding bla(SHV-5) were homologous to plasmid p1658/97 from Escherichia coli, containing a truncated recF gene and a truncated deoR gene upstream and downstream from bla(SHV-5), respectively. RecF may be involved in bla(SHV-5) translocation to the plasmid by RecF-dependent recombination. This novel genetic environment may be associated with the successful proliferation and/or expression of SHV-5 in K. pneumoniae strains from Taiwan.

Base Sequence↗
PubMed1994

IS231 and other Bacillus thuringiensis transposable elements: a review.

Bacillus thuringiensis is an entomopathogenic bacterium whose toxicity is due to the presence in the sporangia of delta-endotoxin crystals active against agricultural pests and vectors of human and animal diseases. Most of the genes coding for these toxin proteins are plasmid-borne and are generally structurally associated with insertion sequences (IS231, IS232, IS240, ISBT1 and ISBT2) and transposons (Tn4430 and Tn5401). Several of these mobile elements have been shown to be active and are believed to participate in the crystal gene mobility, thereby contributing to the variation of bacterial toxicity. Structural analysis of the iso-IS231 elements indicates that they are related to IS1151 from Clostridium perfringens and distantly related to IS4 and IS186 from Escherichia coli. Like the other IS4 family members, they contain a conserved transposase-integrase motif found in other IS families and retroviruses. Moreover, functional data gathered from IS231A in Escherichia coli indicate a non-replicative mode of transposition, with a marked preference for specific targets. Similar results were also obtained in Bacillus subtilis and B. thuringiensis, and a working model for DNA-protein interactions at the target site is proposed.

Amino Acid Sequence↗
PubMed1984

Nucleotide sequence of the transposable element IS15.

We have determined the complete nucleotide sequence of the right (R) copy of the insertion sequence IS15 which flanks, in direct orientation, the composite transposon Tn1525. IS15-R, which is capable of independent transposition, is 1648 bp long and has short (14 bp) perfect inverted repeats at its termini. Analysis of the nucleotide sequence indicates that IS15-R results from the transposition, in direct orientation, of a smaller (820 bp long) IS, designated IS15-delta, into itself. This integration event is accompanied by the duplication of 8 bp in the target DNA. IS15-delta possesses two large overlapping open reading frames (ORF) located on opposite strands. Because of this particular structure, IS15 possesses four large ORFs which, due to the integration event, exhibit some differences with those of the parental IS15-delta.

Base Sequence↗
PubMed1995

Horizontal transmission, vertical inactivation, and stochastic loss of mariner-like transposable elements.

Horizontal transmission has been well documented as a major mechanism for the dissemination of mariner-like elements (MLEs) among species. Less well understood are mechanisms that limit vertical transmission of MLEs resulting in the "spotty" or discontinuous distribution observed in closely related species. In this article we present evidence that the genome of the common ancestor of the melanogaster species subgroup of Drosophila contained an MLE related to the mellifera (honey bee) subfamily. Horizontal transmission, approximately 3-10 MYA, is strongly suggested by the observation that the sequence of the MLE in Drosophila erecta is 97% identical in nucleotide sequence with that of an MLE in the cat flea, Ctenocephalides felis. The D. erecta MLE has a spotty distribution among species in the melanogaster subgroup. The element has a high copy number in D. erecta and D. orena, a moderate copy number in D. teissieri and D. yakuba, and was apparently lost ("stochastic loss") in the lineage leading to D. melanogaster, D. simulans, D. mauritiana, and D. sechellia. In D. erecta, most copies are concentrated in the heterochromatin. Two copies from D. erecta, denoted De12 and De19, were cloned and sequenced, and they appear to be nonfunctional ("vertical inactivation"). It therefore appears that the predominant mode of MLE evolution is vertical inactivation and stochastic loss balanced against occasional reinvasion of lineages by horizontal transmission.

Amino Acid Sequence↗
PubMed2004

Mapping of transposable element Dissociation inserts in Brassica oleracea following plant regeneration from streptomycin selection of callus.

To investigate the potential of heterologous transposons as a gene-tagging system in broccoli (Brassica oleracea var. italica), we have introduced a Dissociation ( Ds)-based two-element transposon system. Ds has been cloned into a 35S-SPT excision-marker system, with transposition being driven by an independent 35S-transposase gene construct. In three successive selfed generations of plants, there was no evidence of germinal-excision events. In a previous study, we overcame this apparent inability to produce B. oleracea plants with germinal excisions by performing a novel tissue-culture technique to select for fully green shoots from seed with somatic excision events. The results showed a very high efficiency of regeneration of fully green plants (up to 65%), and molecular analysis showed that the plants contained the equivalent of a germinal-excision event. In this study, we followed the previous work by using inverse and nested PCR to generate probes of flanking genomic DNA adjacent to independently reinserted Ds elements, and these were hybridised to DNA from a double-haploid mapping population of B. oleracea. Seventeen Ds insertions and the original Ds T-DNA site have been localised, and these are spread over six (out of nine) linkage groups. Distribution of inserts show that 15 were found on a different linkage group to the original 'launch' site, and of these 11 were found to be clustered on two separate groups. Previous studies in other plant species have found that germinal excision of Ds predominantly moves to sites linked close to the donor site. However, this study shows a potential to produce plants with Ds insertion scattered over many unlinked sites.

Blotting, Southern↗
PubMed1990

Active mariner transposable elements are widespread in natural populations of Drosophila simulans.

The occurrence of active, or autonomous, mariner elements was investigated by crossing white-peach mutant Drosophila simulans females with wild-type males from various geographic origins. From a total of 194 experimental crosses only 17 failed to produce progeny with eye mosaicism (MOS, i.e. pigmented spots in otherwise white-peach eyes). Therefore, active mariner elements inducing somatic excision of the copy inserted at the white locus are abundant in all populations sampled. In the experimental crosses the frequency of mosaic offspring ranged from 0 to 100%, showing that the phenotypic expression is highly variable. The MOS phenotype, measured by the number of spots on the eyes, is quite variable within the progeny of single crosses. Although a difference was observed in the average MOS score (percentage of mosaic flies) between northern and southern populations of France, there was no indication of long range variation between geographic populations. Neither was there a systematic difference between recently collected populations and samples kept several years as isofemale lines.

Animals↗
PubMed1990

Regulated splicing of the Drosophila P transposable element third intron in vitro: somatic repression.

In eukaryotic cells alternative splicing of messenger RNA precursors (pre-mRNA's) is a means of regulating gene expression. Although a number of the components that participate in regulating some alternative splicing events have been identified by molecular genetic procedures, the elucidation of the biochemical mechanisms governing alternative splicing requires in vitro reaction systems. The tissue specificity of P element transposition in Drosophila depends on the germline restriction of pre-mRNA splicing of the P element third intron (IVS3). Drosophila P element IVS3 pre-mRNA substrates were spliced accurately in vitro in heterologous human cell extracts but not in Drosophila somatic cell splicing extracts. Components in Drosophila somatic cell extracts that specifically inhibited IVS3 splicing in vitro were detected by a complementation assay. Biochemical assays for Drosophila RNA binding proteins were then used to detect a 97-kilodalton protein that interacts specifically with 5' exon sequences previously implicated in the control of IVS3 splicing in vivo. Inhibition of IVS3 splicing in vitro could be correlated with binding of the 97-kD protein to 5' exon sequences, suggesting that one aspect of IVS3 tissue-specific splicing involves somatic repression by specific RNA-protein interactions.

Animals↗
PubMed1996

Computer simulation of transposable element evolution: random template and strict master models.

It has been proposed that the most extensively studied mammalian retrotransposons replicate by some form of a master template model. This conclusion has been drawn largely from DNA sequence analysis and is based on phylogenetic tree topology, the presence and ordering of shared variants, the degree of divergence between elements within a subfamily, and the shape of the distribution of pairwise differences between elements. To investigate how robust these parameters are as predictors of the model of transposition, computer simulations of the two most extreme transposition models, the Random Template Model and the Strict Master Model, were carried out. A prototype of a computer simulator for studying retrotransposition is presented. The simulator is a versatile digital workbench that maintains DNA sequence data and allows manipulation of a range of factors including reverse transcriptase and in situ mutation rates, transposition template, and transposition rate. All parameters previously used as predictors of the model of transposition were markedly different for the two extreme models when evaluated using large sample sizes of sequences from experiments simulating up to 15 million years of evolution.

Animals↗
PubMed2005

Novel variants of human SCaMC-3, an isoform of the ATP-Mg/P(i) mitochondrial carrier, generated by alternative splicing from 3'-flanking transposable elements.

CaMCs (calcium-dependent mitochondrial carriers) represent a novel subfamily of metabolite carriers of mitochondria. The ATP-Mg/P(i) co-transporter, functionally characterized more than 20 years ago, has been identified to be a CaMC member. There are three isoforms of the ATP-Mg/P(i) carrier in mammals, SCaMC-1 (short CaMC-1), -2 and -3 (or APC-1, -3 and -2 respectively), corresponding to the genes SLC25A24, SLC25A25 and SLC25A23 respectively, as well as six N-terminal variants generated by alternative splicing for SCaMC-1 and -2 isoforms. In the present study, we describe four new variants of human SCaMC-3 generated by alternative splicing. The new mRNAs use the exon 9 3'-donor site and distinct 5'-acceptor sites from repetitive elements, in regions downstream of exon 10, the last exon in all SCaMCs. Transcripts lacking exon 10 (SCaMC-3b, -3b', -3c and -3d) code for shortened proteins lacking the last transmembrane domain of 422, 456 and 435 amino acids, and were found in human tissues and HEK-293T cells. Mitochondrial targeting of overexpressed SCaMC-3 variants is incomplete. Surprisingly, the import impairment is overcome by removing the N-terminal extension of these proteins, suggesting that the hydrophilic N-terminal domain also participates in the mitochondrial import process, as shown for the CaMC members aralar and citrin [Roesch, Hynds, Varga, Tranebjaerg and Koehler (2004) Hum. Mol. Genet. 13, 2101-2111].

3' Flanking Region↗
PubMed1997

The Clostridium perfringens enterotoxin gene is on a transposable element in type A human food poisoning strains.

The Clostridium perfringens enterotoxin gene (cpe) is rarely found in naturally isolated strains. In human food poisoning strains, cpe is found on the chromosome, and is located episomally in animal isolates. Observations that the gene was somewhat unstable and could be gained or lost suggested that the gene was on a mobile element. An IS200-like element, IS1469, is almost always upstream of cpe. A new insertion element was identified, IS1470, a member of the IS30 family, which is found both up-an downstream of cpe in the type A strain NCTC 8239. PCR results confirmed that this configuration was conserved in type A human food poisoning strains. The enterotoxin gene was on a 6.3 kb transposon which, in addition to the two flanking copies of IS1470, included IS1469 and two 1 kb stretches, one on each side of cpe, with no open reading frames. Results indicated that 14 bp was copied from the genome during insertion. Details of the configuration of DNA in this transposon are presented, and the possible connection of this transposon with the movement of the enterotoxin gene is discussed.

Animals↗
PubMed1990

Action of a transposable element in coding sequence fusions.

The original Casadaban technique for isolating fused cistrons encoding hybrid beta-galactosidase proteins used a Mucts62 prophage to align the upstream coding sequence and lacZ prior to selection. Kinetic analysis of araB-lacZ fusion colony emergence indicated that the required DNA rearrangements were regulated and responsive to conditions on selection plates. This has been cited as an example of "directed mutation." Here we show genetically that the MuA and integration host factor (IHF) transposition functions are involved in the formation of hybrid araB-lacZ cistrons and propose a molecular model for how fusions can form from the initial strand-transfer complex. These results confirm earlier indications of direct Mu involvement in the fusion process. The proposed model explains how rearranged Mu sequences come to be found as interdomain linkers in certain hybrid cistrons and indicates that the fusion process involves a spatially and temporally coordinated sequence of biochemical reactions.

Base Sequence↗
PubMed1988

Overproduction of the protein encoded by the maize transposable element Ac in insect cells by a baculovirus vector.

The polypeptide encoded in the Activator (Ac) element of Zea mays L. has been expressed in Spodoptera frugiperda insect cells using plasmids which carry the strong polyhedrin promoter of the baculovirus Autographa californica nuclear polyhedrosis virus (AcNPV). Recombinant AcNPVs with the Ac-cDNA integrated and under the control of the viral polyhedrin promoter have been isolated and their genomes have been partly characterized as to the location of the foreign DNA insert. Upon infection of S. frugiperda cells with the recombinant AcNPV, maize Ac element specific messenger RNAs, as well as a newly synthesized polypeptide with an apparent molecular weight of about 116 kDa, have been detected in extracts of recombinant infected cells. This polypeptide is absent from extracts of wild-type infected cells expressing the polyhedrin polypeptide which can be recognized by the presence of nuclear inclusion bodies. Recombinant infected cells lack this protein. The Ac specific polypeptide is detected by antisera, which have been raised against fusion proteins containing Ac sequences synthesized in Escherichia coli, both in immunoprecipitation and in Western blotting experiments. The Ac specific protein is a nuclear phosphoprotein and represents about 1%-2% of the newly synthesized protein.

Animals↗