Electronic Thesis and Dissertation Repository


Master of Science




Dr. Hong Ling


The genome is constantly damaged by intracellular and extracellular factors. At sites of DNA damage, replication forks are stalled, leading monoubiquitination of proliferating cell nuclear antigen (PCNA). Monoubiquitination of PCNA promote the switch from regular high-fidelity polymerases to Y-family polymerases for bypassing damaged DNA. Prolonged replication by these polymerases may lead to increased mutagenesis, so tight regulation of this process is required. ATAD5 recruits a deubiquitinase complex consisting of ubiquitin-specific protease 1 (USP1) and USP1-associated factor 1 (UAF1) to control PCNA monoubiquitination. The mechanism by which ATAD5 and PCNA interact has been previously unexplored. We show through biochemical and structural studies that ATAD5 contains a non-canonical PCNA-interacting protein motif that interacts with PCNA in the low µM range. Our structural studies indicate that the binding of ATAD5’s PIP Box to PCNA is topologically conserved with respect to canonical PIP Boxes from other proteins. Furthermore, we detected weak interactions between ATAD5’s and UAF1’s protein interacting motifs. This suggests that ATAD5 acts as an adapter between PCNA and the UAF1-USP1 deubiquitinase complex. Characterization of these interactions will increase our understanding of DNA damage tolerance and may lead to the design of better cancer therapeutics.