Catalytic subunit of the DNA polymerase alpha complex (also known as the alpha DNA polymerase-primase complex) which plays an essential role in the initiation of DNA synthesis (PubMed:9858578, PubMed:6773966, PubMed:6806812, PubMed:6403945, PubMed:6409898). During the S phase of the cell cycle, the DNA polymerase alpha complex (composed of a catalytic subunit PolA1, an accessory subunit PolA2 and two primase subunits, the catalytic subunit Prim1 and the regulatory subunit Prim2) is recruited to DNA at the replicative forks (PubMed:9858578, PubMed:6773966, PubMed:6806812, PubMed:6409898). The primase subunit of the polymerase alpha complex initiates DNA synthesis by oligomerising short RNA primers on both leading and lagging strands (By similarity). These primers are initially extended by the polymerase alpha catalytic subunit and subsequently transferred to polymerase delta and polymerase epsilon for processive synthesis on the lagging and leading strand, respectively (By similarity). In addition to polymerase activity, exhibits 3' to 5' exonuclease activity (PubMed:3112771, PubMed:3129427). a 2'-deoxyribonucleoside 5'-triphosphate + DNA(n) = diphosphate + DNA(n+1) Inhibited by N2-(p-n-butylphenyl) deoxyguanosine 5'-triphosphate and N2-(p-n-butylphenyl) deoxyadenosine 5'-triphosphate (PubMed:3129427). DNA synthesis is not inhibited by fungal toxin alpha-amaitin (PubMed:6806812). The 3'-5' exonuclease activity is inhibited by 10mM dGMP (PubMed:3129427). Component of the alpha DNA polymerase complex (also known as the alpha DNA polymerase-primase complex) consisting of four subunits: the catalytic subunit PolA1, the regulatory subunit PolA2, and the primase complex subunits Prim1 and Prim2 respectively (PubMed:6773966, PubMed:6403945, PubMed:6409898, PubMed:7592543). PolA1 associates with the DNA primase complex before association with PolA2 (PubMed:6409898). Interacts with Dpit47; the interaction inhibits the activity of the DNA polymerase and occurs only in proliferating cells but not in quiescent cells (PubMed:11493638). Expressed in embryos (at protein level). Expressed both maternally and zygotically. Highest level of zygotic expression seen in second-instar larva, level is reduced at other stages of development. The CysA-type zinc finger is required for PCNA-binding. In embryos, a cleaved form of 130 kDa is produced up to cycle 14 and then disappears. In eukaryotes there are five DNA polymerases: alpha, beta, gamma, delta, and epsilon which are responsible for different reactions of DNA synthesis. Belongs to the DNA polymerase type-B family.