Abstract
The 'proliferating cell nuclear antigen' (PCNA), also known as cyclin, appears at the G1/S boundary in the cell cycle. Because of its possible relationship with cell proliferation, PCNA/cyclin has been receiving attention. PCNA/cyclin is a non-histone acidic nuclear protein with an apparent mol. wt of 33000-36000. The amino acid composition and the sequence of the first 25 amino acids of rabbit PCNA/cyclin are known. Using an oligonucleotide probe corresponding to the sequence of the first five amino acids, a cDNA clone for PCNA/cyclin was isolated from rat thymocyte cDNA library. The cDNA (1195 bases) contains an open reading frame of 813 nucleotides coding for 261 amino acids. The 3'-non-coding region is 312 nucleotides long and contains three putative polyadenylation signals. The mol. wt of rat PCNA/cyclin was calculated to be 28 748. The deduced amino acid sequence and composition of rat PCNA/cyclin are in excellent agreement with the published data. Using the cDNA probe, two species of mRNA (1.1 and 0.98 kb) were detected in rat thymocyte RNA. Southern blot analysis of total human genomic DNA suggests that there is a single gene coding for PCNA/cyclin. The deduced amino acid sequence of rat PCNA/cyclin has a similarity with that of herpes simplex virus type-1 DNA binding protein.