Phylogenetic analysis of archaeal PCNA homologues

Proliferating cell nuclear antigen (PCNA) is an essential component of the DNA replication and repair machinery in the domain Eucarya. Eukaryotes and euryarchaeotes, which belong to one subdomain of Archaea, possess a single PCNA homologue, whereas two distinct PCNA homologues have been identified f rom Sulfolobus solfataricus, which belongs to the other archaeal subdomain, Crenarchaeota. We have cloned and sequenced two genes of PCNA homologues f rom the thermoacidophilic crenarchaeon Sulfurisphaera ohwakuensis. These ge nes, referred to as the Soh PCNA A gene and the Soh PCNA B gene, were found to encode 245 amino acids (aa) (27kDa) and 248 aa(27kDa), respectively. In deduced amino acid sequences of both PCNA homologues, the motif L/I-A-P-K/ R, implicated in binding of PCNA with replication factor C (RFC), was ident ified. Phylogenetic analysis of all available archaeal PCNA homologues sugg ests that crenarchaeal homologues are divided into two groups. Group A cons ists of Soh PCNA A, one of the S. solfataricus PCNA homologues, and one of the Aeropyrum pernix PCNA homologues. The other crenarchaeal homologues for m group B. Crenarchaeal PCNA homologues constitute a monophyletic subfamily . These results suggest that the evolution of crenarchaeal PCNA homologues has been characterized by one or two gene duplication events, which are ass umed to have occurred after the split of the crenarchaeal and euryarchaeal lineages.