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We have investigated the expression of two Schizosaccharomyces pombe replicative DNA polymerases a and 6 during the cell cycle. The pola' and pol6+ genes encoding DNA polymerases a and 6 were isolated from S. pombe. Both pola' and pol6+ genes are single copy genes in haploid cells and are essential for cell viability. In contrast to Saccharomyces cerevisiae homologs, the steady-state transcripts of both S. pombe pola' and pol6+ genes were present throughout the cell cycle. Sequence analysis of the pola' and pol6+ genes did not reveal the Mlu I motifs in their upstream sequences that are involved in cell cycledependent transcription of S. cerevisiae DNA synthesis genes as well as the S. pombe cdc22+ gene at the G1/S boundary. However, five near-match Mlu I motifs were found in the upstream region of the pola' gene. S. pombe DNA polymerases a and 6 proteins were also expressed constantly throughout the cell cycle. In addition, the enzymatic activity of the S. pombe DNA polymerase a measured by in vitro assay was detected at all stages of the cell cycle. Thus, these S. pombe replicative DNA polymerases, like that of S. pombe cdc17+ gene, are expressed throughout the cell cycle at the transcriptional and protein level. These results indicate that S. pombe has at least two regulatory modes for the expression of genes involved in DNA replication and DNA precursor synthesis.

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