Telomere replication has been proposed to be involved in tumor genesis. However, it is not clear how telomeres are maintained and replicated. Bud yeast is an excellent model system to study telomere biology because of the considerable conservation of telomere structure and function. Cdc13p is a cell division protein in S. cerevisiae (bud yeast). It can bind telomeric DNA in vitro. Mutation studies have suggested that Cdc13p might bind telomeres in vivo, limit strand specific telomere degradation and recruit telomerase to the telomere. In order to understand the mechanism of telomere replication and the roles of Cdc13p in this procession, a number of proteins that interact with Cdc13p in a two-hybrid system have been identified. In this proposal, these interactions between Cdc13p and candidates will be confirmed by biochemical and genetic approaches, and the importance of these interactions will be studied by disrupting the interactions using mutations. The sub-cellular locations of Cdc13p will be determined by GFP-fluorescence and immuno-fluorescence. The effect of Cdc13p interacting protein on its cellular location will also be studied. This work might reveal the mechanism of telomere replication and shall shed light on human telomere biology.