INACTIVATION OF DNA-POLYMERASE BETA BY INVITRO PHOSPHORYLATION WITH PROTEIN-KINASE-C

The M(r) = 38,300 polypeptide of the purified recombinant rat DNA polymerase-beta served as an excellent substrate for protein kinase C (PKC) in vitro but not for the catalytic subunit of cAMP-dependent protein kinase. The phosphorylation by PKC resulted in inactivation of DNA polymerase beta-activity, and recovery was achieved by dephosphorylation with alkaline phosphatase. Since the phosphorylated DNA polymerase-beta was retained with use of a single-stranded DNA-cellulose column, inactivation might occur at a site different from that for the DNA binding. Amino acid sequence analysis of the phosphopeptides revealed that the phosphorylated sites were 2 serine residues at positions 44 and 55 from the NH2 terminus, either or both of which might be involved in the catalytic activity of DNA polymerase-beta. Thus, the inactivation of the DNA repair enzyme, DNA polymerase-beta, by PKC may be an important process in the modification of DNA metabolism in the nucleus through signal transduction processes.