Saccharomyces cerevisiae telomeres. A review

Recent work has yielded considerable information concerning the structure and function of telomeres and their associated sequences in the budding yeast Saccharomyces cerevisiae. The structure and maintenance of telomeres depends not only on the RNA template and the catalytic subunit of telomerase, but on a number of other proteins. These include proteins involved in assessing DNA damage and cell cycle regulation. There are also non-telomerase mediated processes involved in the normal maintenance of telomeres. In addition to proteins involved in telomere maintenance, there are a number of other proteins involved in the chromatin structure of the region. Many of these proteins have roles in silencing, ageing, segregation and nuclear architecture. The structure of the subtelomeric regions has been well characterized and consists of a mosaic of repeats found in variable copy numbers and locations. Amidst the variable mosaic elements there are small conserved sequences found at all ends that may have functional roles. Recent work shows that the subtelomeric repeats can rescue chromosome ends when telomerase fails, buffer subtelomerically located genes against transcriptional silencing, and protect the genome from deleterious rearrangements due to ectopic recombination. Thus the telomeres of yeast have a variety of roles in the life of the yeast cell beyond the protection of the ends and overcoming the end replication problem associated with linear molecules.