ISSN:
1432-1432
Keywords:
HeT-A
;
Telomere
;
Retrotransposon
;
Translational frameshift
;
gag proteins
;
Zinc knuckle
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract A major component of Drosophila telomeres is the retrotransposonHeT-A, which is clearly related to other retrotransposons and retroviruses. This retrotransposon is distinguished by its exclusively telomeric location, and by the fact that, unlike other retrotransposons, it does not encode its own reverse transcriptase.HeT-A coding sequences diverge significantly, even between elements within the same genome. Such rapid divergence has been noted previously in studies ofgag genes from other retroelements. Sequence comparisons indicate that the entireHeT-A coding region codes forgag protein, with regions of similarity to other insect retrotransposongag proteins found throughout the open reading frame (ORF). Similarity is most striking in the zinc knuckle region, a region characteristic ofgag genes of most replication-competent retroelements. We identify a subgroup of insect non-LTR retrotransposons with three zinc knuckles of the form: (1) CX2CX4HX4C, (2) CX2CX3HX4C, (3) CX2CX3HX6C. The first and third knuckles are invariant, but the second shows some differences between members of this subgroup. This subgroup includesHeT-A and a second Drosophila telomeric retrotransposon,TART. Unlike other gag regions,HeT-A requires a −1 frameshift for complete translation. Such frameshifts are common between thegag andpol sequences of retroviruses but have not before been seen within agag sequence. The frameshift allowsHeT-A to encode two polypeptides; this mechanism may substitute for the post-translational cleavage that creates multiplegag polypeptides in retroviruses.D. melanogaster HeT-A coding sequences have a polymorphic region with insertions/deletions of 1–31 codons and many nucleotide changes. None of these changes interrupt the open reading frame, arguing that only elements with translatable ORFs can be incorporated into the chromosomes. PerhapsHeT-A translation products act incis to target the RNA to chromosome ends.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02202105
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