CELL CYCLE-DEPENDENT PHOSPHORYLATION AND DEPHOSPHORYLATION OF THE YEAST DNA-POLYMERASE ALPHA-PRIMASE B-SUBUNIT

The yeast DNA polymerase alpha-primase B subunit functions in initiati on of DNA replication. This protein is present in two forms, of 86 and 91 kDa, and the p91 polypeptide results from cell cycle-regulated pho sphorylation of p86. The B subunit present in G(1) arises by dephospho rylation of p91 while cells are exiting from mitosis, becomes phosphor ylated in early S phase, and is competent and sufficient to initiate D NA replication. The B subunit transiently synthesized as a consequence of periodic transcription of the POL12 gene is phosphorylated no earl ier than G(2). Phosphorylation of the B subunit does not require execu tion of the CDC7-dependent step and ongoing DNA synthesis. We suggest that posttranslational modifications of the B subunit might modulate t he role of DNA polymerase ol primase in DNA replication.