Elucidation of Snm1B Function
The protein Snm1B binds to the telomere binding protein TRF2 to help protect telomeres from DNA damage during S phase. In addition, Snm1B protects DNA from agents that induce interstrand crosslinks (ICLs), lethal lesions that covalently attach the opposite strands of DNA together. To elucidate how Snm1B performs these functions I performed a yeast two-hybrid screen to identify proteins binding to the C-terminus of Snm1B. From this screen I identified PSF2 (GINS2), a member of the tetrameric protein complex GINS, to bind Snm1B. The GINS complex is required for replication initiation and elongation. Of interest, the knockdown of PSF2 sensitizes cells to ICL inducing agents. I therefore tested the interaction of PSF2 and Snm1B by co-immunoprecipitation from human cells and discovered that PSF2 binds to two regions of Snm1B. Deletion of the first of these regions inhibited the ability of Snm1B to co-immunoprecipitate with the protein Mus81, a structure specific endonuclease that is required to form double strand breaks (DSBs) as an intermediate in ICL repair. Deletion of the second binding region reduced the ability of PSF2 to localize Snm1B onto chromatin. These data support a role for an interaction of Snm1B with PSF2 in ICL repair.
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