Establishing the role of Elg1-Stn1 interaction in the negative regulation of telomere length in Saccharomyces cerevisiae

In budding yeast, Cdc13, Stn1, and Ten1 forms a heterotrimeric complex (CST) that is essential for telomere protection and maintenance. The recruitment of telomerase complex by Cdc13 promotes telomere elongation, while the formation of Cdc13-Stn1-Ten1 (CST) complex at the telomere blocks telomere elongation by telomerase. Elg1p, a replication factor C (RFC)-like protein of yeast, which is the principal unloader of chromatin-bound PCNA, participates in negative control of telomere length and in telomeric silencing through a replication-mediated pathway. Here, we are trying to establish the mechanism by which Elg1 along with CST complex participates in the regulation of telomere length. Our finding from Yeast Two Hybrid suggest that the C-terminal domain of Stn1, known to be involved in regulating telomere length, interacts strongly with the N-terminal domain of Elg1 and the interaction is dependent on SUMOylation and the SUMO-Interactive Motif (SIM) of Elg1. Futhermore, Stn1 precipitates along with Elg1 in CoIP and this interaction between Stn1 and Elg1 occurs exclusively during the late S-phase and early G2 phase of the cell cycle, where the telomeric regulation occurs, indicating both the protein to be working together in this pathway. This work will further uncover the following events, when the DNA Polymerase I reaches the chromosome end.