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.