A conserved sequence motif within the exceptionally diverse telomeric sequences of budding yeasts

Abstract

Telomeric DNA sequences have generally been found to be remarkably conserved in evolution, typically consisting of repeated, very short sequence units containing clusters of G residues. Recently however the telomeric DNA of the asexual yeast Candida albicans was shown to consist of much longer repeat units. Here we report the identification of seven additional telomeric sequences from sexual and asexual budding yeast species. The telomeric repeat units from this group of relatively closely related species show more phylogenetic diversity in length (8-25 bp), sequence, and composition than has been seen previously throughout a wide phylogenetic range of other eukaryotes. We also show that certain strains of the asexual diploid species Candida tropicalis have two forms of telomeric repeats, which appear to differ by a single base pair. Despite their great diversity, the telomeric repeat units of C. albicans, Saccharomyces cerevisiae, and all of the species we have examined in this report share a conserved ≃6-bp motif of T and G residues resembling more typical telomeric sequences.