De novosynthesis of budding yeast DNA polymerase alpha andPOL1transcription at the G1/S boundary are not required for entrance into S phase

The POL1 gene, encoding DNA polymerase α(pol α) inSaccharomyces cerevisiae, is transiently transcribed during the cell cycle at the G1/S phase boundary. Here we show that yeast pol α is present at every stage of the cell cycle, and its level only slightly increases following the peak ofPOL1transcription.POL1mRNA synthesis driven by aGAL1promoter can be completely abolished without affecting the growth rate of logarithmically growing yeast cultures for several cell divisions, although the amount of the pol α polypeptide drops below the physiological level. Moreover, α-factor-arrested cells can enter S phase and divide synchronously even ifPOL1transcription is abolished. These results indicate that the level of yeast pol α is not rate limiting andde novosynthesis of the enzyme is not required for entrance into S phase.