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At least 955 records · Page 53Linked to original sources
PubMed2006

Use of the transposable element Ac/Ds in conjunction with Spm/dSpm for gene tagging allows extensive genome coverage with a limited number of starter lines: functional analysis of a four-element system in Arabidopsis thaliana.

We have developed a novel four-element based gene tagging system in Arabidopsis to minimize the number of starter lines required to generate genome-wide insertions for saturation mutagenesis. In this system, the non-autonomous cassette, Ds(dSpm), comprises of both Ds and dSpm elements cloned one within the other along with appropriate selection markers to allow efficient monitoring of excision and re-integration of the transposons. Trans-activation of the outer borders (Ds) and selection against the negative selection marker (iaaH) linked to the cassette ensures unlinked spread of the Ds(dSpm) cassette from the initial site of integration of the T-DNA. This creates several launch pads within the genome from where the internal element (dSpm) can be subsequently mobilized to generate secondary insertions. In this study, starting from a single T-DNA integration we could spread the Ds(dSpm) cassette to 11 different locations over all the five chromosomes of Arabidopsis. The frequency of unlinked Ds transpositions in the F2 generation varied between 0.05 and 3.35%. Three of these lines were then deployed to trans-activate the internal dSpm element which led to the selection of 29 dSpm insertions. The study conclusively shows the feasibility of deploying Ds and the dSpm elements in a single construct for insertional mutagenesis.

Arabidopsis↗
PubMed1983

Transposable element IS50 improves growth rate of E. coli cells without transposition.

Insertion sequence IS50R, which encodes the transposase and an inhibitor of transposition of the kanamycin-resistance transposon Tn5, increases the growth rate of E. coli K12 cells relative to that of their otherwise isogenic counterparts during competition in continuous culture. Most clones isolated from chemostats in which selection had occurred retain their original number of copies of IS50R at their original genomic locations, implying that the increased growth rate is not mediated by transposition. The selective advantage due to a single IS50R element averages about 5% per hour. When the number of copies of IS50R is small, the growth-rate advantage is approximately proportional to the number of copies of IS50R. These results imply that IS50R has effects on cells that are independent of both position and transposition and may be important in the initial selection leading to the appearance of such elements in bacterial populations.

Chromosomes, Bacterial↗
PubMed1986

Terminal inverted repeats of prokaryotic transposable element IS186 which can generate duplications of variable length at an identical target sequence.

The insertion element IS186, which resides in the chromosome of Escherichia coli K-12, is 1338 bp long. Its termini represent 23-bp perfectly inverted repeats, but a variant carries a mismatch at position 23. IS186 transposes preferentially into G + C-rich sequences and generates target duplications of variable length, even at the same integration site.

Base Composition↗
PubMed1993

DNA sequence and transcript analysis of transposon MuA2, a regulator of Mutator transposable element activity in maize.

The 4942 bp DNA sequence of Zea mays transposon MuA2 was determined. Previous evidence indicated MuA2 controls activity of the Mu1 transposon located in the mutable allele a1-mum2. MuA2 contains two large, ATG-initiated open reading frames (ORFs) of 612 and 232 codons, respectively, located on opposite strands. MuA2 produces two transcripts, each containing one of these ORFs. Four different tandem direct repeat sequences are located downstream of the 612 codon ORF. The restriction map of MuA2 is identical to that of transposon MuR1, which also is known to regulate mutability of a1-mum2. Furthermore, except for a single nucleotide, MuA2 is identical to the Mutator element Mu9.

Amino Acid Sequence↗
PubMed2006

Mavericks, a novel class of giant transposable elements widespread in eukaryotes and related to DNA viruses.

We previously identified a group of atypical mobile elements designated Mavericks from the nematodes Caenorhabditis elegans and C. briggsae and the zebrafish Danio rerio. Here we present the results of comprehensive database searches of the genome sequences available, which reveal that Mavericks are widespread in invertebrates and non-mammalian vertebrates but show a patchy distribution in non-animal species, being present in the fungi Glomus intraradices and Phakopsora pachyrhizi and in several single-celled eukaryotes such as the ciliate Tetrahymena thermophila, the stramenopile Phytophthora infestans and the trichomonad Trichomonas vaginalis, but not detectable in plants. This distribution, together with comparative and phylogenetic analyses of Maverick-encoded proteins, is suggestive of an ancient origin of these elements in eukaryotes followed by lineage-specific losses and/or recurrent episodes of horizontal transmission. In addition, we report that Maverick elements have amplified recently to high copy numbers in T. vaginalis where they now occupy as much as 30% of the genome. Sequence analysis confirms that most Mavericks encode a retroviral-like integrase, but lack other open reading frames typically found in retroelements. Nevertheless, the length and conservation of the target site duplication created upon Maverick insertion (5- or 6-bp) is consistent with a role of the integrase-like protein in the integration of a double-stranded DNA transposition intermediate. Mavericks also display long terminal-inverted repeats but do not contain ORFs similar to proteins encoded by DNA transposons. Instead, Mavericks encode a conserved set of 5 to 9 genes (in addition to the integrase) that are predicted to encode proteins with homology to replication and packaging proteins of some bacteriophages and diverse eukaryotic double-stranded DNA viruses, including a DNA polymerase B homolog and putative capsid proteins. Based on these and other structural similarities, we speculate that Mavericks represent an evolutionary missing link between seemingly disparate invasive DNA elements that include bacteriophages, adenoviruses and eukaryotic linear plasmids.

Amino Acid Sequence↗
PubMed1988

Meiotic recombination between repeated transposable elements in Saccharomyces cerevisiae.

We have measured the frequency of meiotic recombination between marked Ty elements in the Saccharomyces cerevisiae genome. These recombination events were usually nonreciprocal (gene conversions) and sometimes involved nonhomologous chromosomes. The frequency of ectopic gene conversion among Ty elements appeared lower than expected on the basis of previous studies of recombination between artificially constructed repeats. The conversion events involved either a subset of the total Ty elements in the genome or the conversion tract was restricted to a small region of the Ty element. In addition, the observed conversion events were very infrequently associated with reciprocal exchange.

DNA↗
PubMed2000

Playing second fiddle: second-strand processing and liberation of transposable elements from donor DNA.

Retroviruses and many transposons of both prokaryotes and eukaryotes share similar chemical reactions in their transposition. Some elements remain attached to donor DNA during transposition and their translocation results in a fusion between target and donor replicons. However, many elements are separated from their flanking donor DNA prior to their insertion into a target site, which requires processing of both strands at both ends of the element. A variety of strategies have been adopted for cleavage of the second, complementary strand to liberate the transposon.

Animals↗
PubMed1997

Foldback transposable elements in plants.

A novel transposon family was discovered in plants. This family, designated SoFT (Solanaceae Foldback Transposon), exhibit striking structural similarity to the 'foldback' class of animal transposons. SoFT elements consist of a middle segment surrounded by long terminal inverted repeats. Two of the identified SoFT elements have 'classical' foldback structure: their inverted repeats are divided into two domains. The outer domain consists of tandemly arranged subrepeats, whereas the inner domain is non-repetitive and AT-rich. The existence of foldback elements in plants as well as in animals suggests that long inverted repeat (foldback) transposons are ubiquitous among eukaryotes.

Animals↗
PubMed1987

Evolution of P transposable elements: sequences of Drosophila nebulosa P elements.

P elements have been cloned and sequenced from Drosophila nebulosa. Their sequences have diverged less than 6% from P elements of Drosophila melanogaster. However D. nebulosa P elements have nucleotide changes that close all four open reading frames found in the D. melanogaster P element. Microinjection experiments show that D. nebulosa P elements cannot provide transposase function for D. melanogaster P elements, nor are D. nebulosa P elements mobilized by the transposase provided by a D. melanogaster P factor. Three D. nebulosa P elements appear to have integrated into the same position of a complex, centromeric repeated sequence. Comparison of nucleotide sequences suggests that D. nebulosa P elements have diverged upon different pathways from a common ancestor that was 99% homologous to the P elements of D. melanogaster.

Base Sequence↗