InterPro domain: IPR007238

DNA primase is the polymerase that synthesises small RNA primers for the Okazaki fragments made during discontinuous DNA replication. Primases are grouped into two classes, bacteria/bacteriophage and archaeal/eukaryotic. The proteins in the two classes differ in structure and the replication apparatus components. Archaeal/eukaryotic core primase is a heterodimeric enzyme consisting of a small catalytic subunit (PriS or Pri1) and a large subunit (PriL or Pri2). In the yeast Saccharomyces cerevisiae the small subunit is 48kDa and the large subunit 58kDa [ 1 ]. In eukaryotic organisms, a heterotetrameric enzyme formed by DNA polymerase alpha, the B subunit and two primase subunits has primase activity. Although the catalytic activity and the the ATP binding site reside within PriS [ 2 ], the PriL subunit is essential for primase function as disruption of the PriL gene in yeast is lethal. PriL is composed of two structural domains. Several functions have been proposed for PriL such as stabilization of the PriS, involvement in synthesis initiation, improvement of primase processivity, determination of product size and transfer of the products to DNA polymerase alpha [ 3 ]. Primase function has also been demonstrated for human and mouse primase subunits [ 4 ].

1. A single essential gene, PRI2, encodes the large subunit of DNA primase in Saccharomyces cerevisiae. Mol. Cell. Biol. 9, 3081-7
2. Mutations in conserved yeast DNA primase domains impair DNA replication in vivo. Proc. Natl. Acad. Sci. U.S.A. 88, 3877-81
3. Structure of the heterodimeric core primase. Nat. Struct. Mol. Biol. 12, 1137-44
4. DNA replication in vitro by recombinant DNA-polymerase-alpha-primase. Eur. J. Biochem. 222, 781-93