Date of Award
de Lange Laboratory
Members of the β-CASP family of proteins are involved in DNA repair and RNA processing. We identified a member of this family of enzymes, hSNM1B/Apollo, in complex with the telomere binding proteins TRF2/Rap1. Due to its low abundance at telomeres, we consider Apollo to be a telomere accessory factor, and not part of the core telomere protein complex, shelterin. Apollo localizes to telomeres by interacting directly with the TRFH domain of TRF2. Structural analysis of this interaction revealed an interface in the TRFH domain of TRF2 that is predicted to be shared by numerous accessory factors recruited to the telomere by TRF2, in addition to Apollo. Disruption of the Apollo-TRF2 interaction by expressing an allele of Apollo that cannot bind to TRF2 (ApolloΔTRF2) or reducing the amount of endogenous Apollo in cells by RNAi resulted in deprotection of telomeres in S-phase, as evidenced by the presence of Telomere-dysfunction Induced Foci (TIFs). Additionally, Apollo-deficient telomeres have an aberrant signal seen by FISH that is more frequent after treatment with the DNA replication inhibitor, Aphidicolin. Together, the data are consistent with a role for Apollo during of after telomere replication. Isolation of the Apollo protein complex revealed that soluble Apollo is complexed in 1:1 stoichiometry with TRF2/Rap1, suggesting that Apollo might function primarily at telomeres. Additional components include DBC- 1, which interacts directly with Apollo and localizes to Cajal bodies, the translesion synthesis polymerase polη, and the homolgous recombination factor Rad51. The association of these proteins with Apollo suggests potential roles for Apollo in telomerase recruitment and formation of the protective t-loop structure at chromosome ends.
van Overbeek, Megan, "The Apollo Nuclease Binds To TRF2 and Protects" (2008). Student Theses and Dissertations. 219.