Phosphorylation of the DNA polymerase alpha-primase B subunit is dependent on its association with the p180 polypeptide

The B subunit of the DNA polymerase (pol) α-primase complex executes an essential role at the initial stage of DNA replication in Saccharomyces cerevisiae and is phosphorylated in a cell cycle-dependent manner. In this report, we show that the four subunits of the yeast DNA polymerase α- primase complex are assembled throughout the cell cycle, and physical association between newly synthesized pol α (p180) and unphosphorylated B subunit (p86) occurs very rapidly. Therefore, B subunit phosphorylation does not appear to modulate p180·p86 interaction. Conversely, by depletion experiments and by using a yeast mutant strain, which produces a low and constitutive level of the p180 polypeptide, we found that formation of the p180·p86 subcomplex is required for B subunit phosphorylation.