Some transposable elements can be beneficial and others may persist in the genomes of sexually reproducing eukaryotes even if they are deleterious. In the December 4 Proceedings of the National Academy of Sciences, Irina Arkhipova and Hilary Morrison report the characterization of retrotransposons in the Giardia lamblia genome (Proc Natl Acad Sci USA 2001, 98:14497-14502).

G. lamblia is a protozoan parasite, one of the earliest-branching eukaryotes, and is thought to be asexual. Arkhipova and Morrison detected three non-LTR (long terminal repeat) retrotransposons families (named GilM, GilT and GilD) in the Giardia genome. The GilM and GilT families are confined to immediate subtelomeric regions; the GilD family appears to be functionally 'dead' as a result of multiple deletions and point mutations. Thus, the protozoan genome appears to lack active deleterious transposons.

The authors propose that Giardia telomeric transposable elements may help to protect chromosome ends, like those of...