We have isolated cDNA clones encoding the human DNA polymerase alpha catalytic polypeptide. Studies of the human DNA polymerase alpha steady-state mRNA levels in quiescent cells stimulated to proliferate, or normal cells compared to transformed cells, demonstrate that the polymerase alpha mRNA, like its enzymatic activity and de novo protein synthesis, positively correlates with cell proliferation and transformation. Analysis of the deduced 1462-amino-acid sequence reveals six regions of striking similarity to yeast DNA polymerase I and DNA polymerases of bacteriophages T4 and phi 29, herpes family viruses, vaccinia virus and adenovirus. Three of these conserved regions appear to comprise the functional active site required for deoxynucleotide interaction. Two putative DNA interacting domains are also identified.