Box 13.2Telomeres in Drosophila

The text describes the reverse transcriptase reaction carried out by the protein component of telomerase. When the amino acid sequences of telomerases are compared with those of other reverse transcriptases, similarities are seen with the enzymes coded by the non-LTR (long terminal repeat) retroelements called retroposons (Section 2.4.2; Eickbush, 1997). This is a fascinating observation when taken in conjunction with the unusual structure of the telomeres of Drosophila. These telomeres are not made up of the short repeated sequences seen in most other organisms, but instead consist of tandem arrays of much longer repeats, 6 or 10 kb in length. These repeats are full-length copies of two typical retroposons, related to LINE-1 of humans, called HeT-A and TART (Pardue et al., 1996). It is not known how these telomeres are maintained, but it is conceivable that the process is analogous to that carried out by telomerase, with a template RNA obtained by transcription of the telomeric retroposons being copied by the reverse transcriptase coded by the TART sequences (HeT-A does not have a reverse transcriptase gene).

The unusual structure of the Drosophila telomere could simply be a quirk of nature, but the attractive possibility that the telomeres of other organisms are degraded retroposons, as suggested by the similarities between telomerase and retroposon reverse transcriptases, cannot be discounted.

From: Chapter 13, Genome Replication

Cover of Genomes
Genomes. 2nd edition.
Brown TA.
Oxford: Wiley-Liss; 2002.
Copyright © 2002, Garland Science.

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