p12DOC1, a growth suppressor, associates with DNA polymerase α/primase

p12DOC-1 is a growth suppressor identified and isolated from normal keratinocytes. Ectopic expression of p12DOC-1 in squamous carcinoma cells led to the reversion of in vitro transformation phenotypes including anchorage independence, doubling time, and morphology. Here we report that p12DOC-1 associates with DNA polymerase α/primase (pol-α:primase) in vitro and in cells. The pol-α:primase binding domain in p12DOC-1 is mapped to the amino-terminal six amino acid (MSYKPN). The biological effect of p12DOC-1 on pol-α:primase was examined using in vitro DNA replication assays. Using the SV40 DNA replication assay, p12DOC-1 suppresses DNA replication, leveling at ∼50%. Similar results were obtained using the M13 single-stranded DNA synthesis assay. Analysis of the DNA replication products revealed that p12DOC-1 affects the initiation step, not the elongation phase. The p12DOC-1 suppression of DNA replication is likely to be mediated either by a direct inhibitory effect on pol-α:primase or by its effect on cycl...