Two distinct proliferating cell nuclear antigens are present in the wheat cell

Proliferating cell nuclear antigen (PCNA) is the processivity factor of the replicative DNA polymerase delta in eukaryotic DNA replication. It is highly conserved in mammals, yeast and plants. Analysis of genome sequences from human, mouse and yeast indicates that the PCNA polypeptide is expressed from a unique gene. Nevertheless in some plants (carrot, maize, tobacco and Arabidopsis) two different PCNA genes have been identified but the polypeptides expressed have not yet been investigated. In this report, we present the first biochemical evidence for the presence of two different PCNA polypeptides in plants. We used chromatographic procedures to detect and purify a short 31 kDa and a long 37 kDa PCNA from cultured wheat cells (Triticum monococcum L.). Their respective C-terminal sequences determined by RT-PCR and 3′ rapid amplification of cDNA ends (3′RACE) indicate that they are encoded by two different genes. The involvement of these two PCNAs in DNA replication is discussed.