Functional Studies of Telomere-Binding Proteins in Saccharomyces castellii

Abstract: Telomeres are the ends of linear eukaryotic chromosomes. The telomeres are essential for solving the end replication problem and they stabilize the genome by protection from degradation. The telomeres also protect the chromosomal ends from by being recognized as DNA breaks by the repair machinery, which could lead to end-to-end fusions. Dysfunctional telomeres are implicated in many complex cellular processes like replicative senescence and tumorgenesis. This clearly indicates the importance of maintenance and length regulation of telomeres. The telomeres are built up by TG-rich tandem repeats and specific proteins binding these repeats. After replication the telomeres can be elongated by the reverse transcriptase, telomerase. In this work an in vitro system that mimics the natural telomere end has been developed. This can be used to investigate the molecular mechanisms involved in the regulation of the telomere length. I have characterized two telomere binding proteins, Rap1 and Cdc13, from the yeast species Saccharomyces castellii. This yeast has properties beneficial for telomere research, like regularly repeated telomeric DNA. The obtained information regarding the binding specificities of S. castellii Rap1 (scasRap1) and S. castellii Cdc13 (scasCdc13) has been used to study the protein interactions. The ability of scasCdc13 to affect telomerase dependent telomere elongation has been investigated as well. Moreover we have shown that these two different classes of telomere-binding proteins act together in order to conserve a telomeric core sequence during evolution.