Transposons in place of telomeric repeats at a Drosophila telomere

Levis, Robert; Ganesan, Robin; Houtchens, Kathleen A.; Tolar, Leigh Anna; Sheen, Fang-miin

doi:10.1016/0092-8674(93)90318-k

Cited by 398 publications

(104 citation statements)

References 63 publications

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“…Retroelements are the major class of interspersed repetitive DNAs in plant and animal genomes. Targeted integration is suggested by their nonrandom distribution, as evidenced by the clustering of retrotransposons in intergenic regions of maize and the association of some retroelements with heterochromatin and telomeres in Drosophila (29)(30)(31)(32). Retroelement targeting, therefore, is likely an important factor in shaping eukaryotic genome organization.…”

Section: Discussionmentioning

confidence: 99%

Silent chromatin determines target preference of the Saccharomyces retrotransposon Ty5

Zou

Voytas

1997

Proc. Natl. Acad. Sci. U.S.A.

108

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The HML and HMR mating loci of Saccharomyces cerevisiae are bound in silent chromatin, which is assembled at the f lanking E and I transcriptional silencers. The retrotransposon Ty5 preferentially integrates into regions of silent chromatin, and Ty5 insertions near the HMR-E silencer account for Ϸ2% of total transposition events. Most Ty5 insertions occur within 800 bp on either side of the autonomously replicating consensus sequence within HMR-E. Ty5 target preference is determined by silent chromatin, because integration near HMR-E is abolished in strains with silencer mutations that alleviate transcriptional repression. The recognition of specific DNA sequences per se does not direct integration, rather, it is the protein complex assembled at the silencers. As demonstrated here for Ty5, recognition of specific chromatin domains may be a general mechanism by which retrotransposons and retroviruses determine integration sites.

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Section: Discussionmentioning

confidence: 99%

Silent chromatin determines target preference of the Saccharomyces retrotransposon Ty5

Zou

Voytas

1997

Proc. Natl. Acad. Sci. U.S.A.

108

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“…Reverse transcription plays a key role in telomere structure, and the enzyme telomerase is a reverse transcriptase that uses an RNA template to synthesize G-rich repeats onto the ends of most eukaryotic chromosomes (21). In Drosophila melanogaster, the non-LTR retrotransposons HeT and TART transpose preferentially to native and broken chromosome ends (22)(23)(24)(25)(26). Reiterative transposition results in tandem arrays of transposons that buffer internal genic sequences from loss through recombination or replication.…”

Section: Discussionmentioning

confidence: 99%

“…Reiterative transposition results in tandem arrays of transposons that buffer internal genic sequences from loss through recombination or replication. These telomeric retrotransposons, therefore, appear to have assumed the role of telomerase-catalyzed repeats in protecting chromosome ends (26). In S. cerevisiae, a second class of subtelomeric repeats, the Y' elements, bear similarity to mobile elements in that they vary in copy number and location among strains (27).…”

Section: Discussionmentioning

confidence: 99%

The Saccharomyces Ty5 retrotransposon family is associated with origins of DNA replication at the telomeres and the silent mating locus HMR.

Zou

Wright

Voytas

1995

Proc. Natl. Acad. Sci. U.S.A.

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We have characterized the genomic organization of the TyS retrotransposons among diverse strains of Saccharomyces cerevisiae and the related species Saccharomyces paradoxus. The S. cerevisiae strain S288C (or its derivatives) carries eight Ty5 insertions. Six of these are located near the telomeres, and five are found within 500 bp of autonomously replicating sequences present in the type X subtelomeric repeat. The remaining two S. cerevisiae elements are adjacent to the silent mating locus HMR and are located within 500 bp of the origin of replication present in the transcriptional silencer HMR-E. Although the S. cerevisiae TyS elements no longer appear capable of transposition, some strains of S. paradoxus have numerous Ty5 insertions, suggesting that transposition is occurring in this species. Most of these elements are adjacent to type X telomeric repeats, and regions flanking four of five characterized S. paradoxus insertions carry autonomously replicating sequences. The genomic organization of the Ty5 elements is in marked contrast to the other S. cerevisiae retrotransposon families (Tyl-4), which are typically located within 500 bp of tRNA genes. For Ty3, this association reflects an interaction between Ty3 and the RNA polymerase III transcription complex, which appears to direct integration [Chalker, D. L. & Sandmeyer, S. B. (1992) Genes Dev. 6, 117-128]. By analogy to Ty3, we predict that Ty5 target choice is specified by interactions with factors present at both the telomeres and HMR that are involved in DNA replication, transcriptional silencing, or the maintenance of the unique chromatin structure at these sites.Retrotransposons are mobile genetic elements that replicate by reverse transcription of an RNA intermediate. The final step in the retrotransposon life cycle is the integration of an element into a new site in the host genome. Integration may be deleterious to the host cell because it can cause mutations or lead to chromosome rearrangements. Mechanisms that minimize this damage preserve the host's genetic integrity and also allow retrotransposons to replicate and maintain viable populations. In the yeast, Saccharomyces cerevisiae mechanisms have evolved that limit the negative consequences of integration by directing transposition to specific sites in the genome.Target preference of the S. cerevisiae retrotransposons has been made strikingly evident by the recent genome sequencing efforts. Insertions of the four best-characterized retrotransposon families (Tyl-4) are found within the nucleotide sequences of chromosomes III and XI (chr III and chr XI, respectively)

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“…Consequently, telomerase expession has been proposed to be required for cellular immortalization . However, other mechanisms of telomere maintenance are also possible (Bryan et al, 1995;Strahl and Blackburn, 1996), such as recombinational events as seen in yeast (Wang and Zakian, 1990) or transposition of retrotransposons as found in Drosophila (Beissmann and Mason, 1992; Levis et al, 1993). Alterations in the regulation of telomerase expression may play a critical role in the immortalization stage of carcinogenesis.…”

Section: Introductionmentioning

confidence: 99%