Crystallographic study of G178S mutant of human proliferating cell nuclear antigen

Proliferating cell nuclear antigen (PCNA) is an evolutionarily conserved protein that forms a ring‐shaped homotrimer that functions as a sliding clamp for DNA replication. The rev6‐1 mutation of Saccharomyces cerevisiae, which inactivates both translesion DNA synthesis and damage‐avoidance pathways while having little effect on normal cell growth, has a G178S substitution in the PCNA protein. Human PCNA protein carrying the G178S substitution was crystallized. Two crystal forms were obtained under similar conditions. Crystal forms I and II belong to space groups P2₁, with unit‐cell parameters a = 84.1, b = 130.2, c = 97.8 Å, β = 113.4°, and P2₁2₁2₁, with unit‐cell parameters a = 68.1, b = 100.2, c = 131.2 Å, respectively. Structural analyses by molecular replacement are now in progress.