Proliferating cell nuclear antigen (PCNA): ringmaster of the genome

Proliferating cell nuclear antigen (PCNA) protein is one of the central mol ecules responsible for decisions of life and death of the cell. The PCNA ge ne is induced by p53, while PCNA protein interacts with p53-controlled prot eins Gadd45, MyD118, CR6 and, most importantly, p21, in the process of deci ding cell fate. If PCNA protein is present in abundance in the cell in the absence of p53, DNA replication occurs. On the other hand, if PCNA protein levels are high in the cell in the presence of p53, DNA repair takes place. If PCNA is rendered non-functional or is absent or present in low quantiti es in the cell, apoptosis occurs. The evolution from prokaryotes to eukaryo tes involved a change of function of PCNA from a 'simple' sliding clamp pro tein of the DNA polymerase complex to an executive molecule controlling cri tical cellular decision pathways. The evolution of multicellular organisms led to the development of multicellular processes such as differentiation, senescence and apoptosis. PCNA, already an essential molecule in the life o f single cellular organisms, then became a protein critical for the surviva l of multicellular organisms.