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 P2(1), with unit-cell parameters a = 84.1, b = 130.2, c = 97.8 A, beta = 113.4 degrees , and P2(1)2(1)2(1), with unit-cell parameters a = 68.1, b = 100.2, c = 131.2 A, respectively. Structural analyses by molecular replacement are now in progress.