This domain is the C-terminal region three-helical domain of primase [1]. Primases synthesise short RNA strands on single-stranded DNA templates, thereby generating the hybrid duplexes required for the initiation of synthesis by DNA polymerases. Primases are recruited to single-stranded DNA by helicases, and this domain is the region of the primase which binds DnaB-helicase [2]. It is associated with the Toprim domain (Pfam:PF01751) which is the central catalytic core.

1: Structure of the RNA polymerase domain of E. coli primase. Keck JL, Roche DD, Lynch AS, Berger JM; Science. 2000;287:2482-2486. PMID:10741967

2: A TOPRIM domain in the crystal structure of the catalytic core of Escherichia coli primase confirms a structural link to DNA topoisomerases. Podobnik M, McInerney P, O'Donnell M, Kuriyan J; J Mol Biol. 2000;300:353-362. PMID:10873470