Abstract
Proliferating cell nuclear antigen (PCNA), an auxiliary factor of DNA polymerase δ, is required in eukaryotic DNA replication and DNA excision repair. PCNA gene expression is growth-regulated. Previously, it has been shown that the proximal AP-1 site (-64 to –58) and an ATF site (-51 to –44) are involved in serum responsiveness of the rat PCNA promoter. When the nuclear proteins of serum-stimulated cells were dephosphoyrlated with alkaline phosphatase, they lost the DNA binding activity, suggesting that protein phosphorylation is involved in modulation of the promoter activity. In this thesis, the involvement of protein phosphorylation in PCNA gene expression was investigated with a phosphatase inhibitor, okadaic acid (OA). The DNA binding activities of transcription factors in rat PCNA promoter increase after OA treatment. PCNA promoter activity and gene expression also increase after OA treatment. These effects may be correlated with the DNA binding activity of AP-1.