DNA replication is an essential task to all life. To ensure precise genome duplication, cells utilize a network of factors that copy, surveil, and repair DNA. The coordination of all these factors heavily relies on the homotrimeric sliding clamp protein, Proliferating Cell Nuclear Antigen (PCNA). Like other sliding clamps, PCNA slides along DNA and acts as a molecular tether that increases the processivity of various DNA-acting enzymes. In addition, PCNA plays a much more multifaceted role in coordinating the concerted efforts of dozens of proteins involved in DNA replication, DNA repair, chromatin remodeling, cell cycle, and apoptosis. Proper interactions with PCNA are necessary for these enzymes to perform their functions. Yet, how PCNA controls its vast network remains unclear. How does partner binding affinity, PCNA levels, and lifetime on DNA influence PCNA’s ability to coordinate various DNA metabolic events? To understand the biophysical principles behind these questions, I investigated how two disease-associated substitutions in PCNA impact partner binding, stability, and its loading onto DNA. Furthermore, I made C. elegans strains that harbored these substitutions to understand their effects at the organismal level. Finally, I identified an electrostatic patch within PCNA that plays a role in partner binding affinity. My work collectively identifies residues that are critical for PCNA function. More broadly, my work provides insight into the evolution of PCNA and how substitutions impact both genome stability and human health.