RNA polymerase that catalyzes the synthesis of short RNA molecules used as primers for DNA polymerase during DNA replication. ssDNA + n NTP = ssDNA/pppN(pN)n-1 hybrid + (n-1) diphosphate. Binds 1 zinc ion per monomer. Binds two Mg(2+) per subunit. Monomer. Interacts with DnaB. Contains an N-terminal zinc-binding domain, a central core domain that contains the primase activity, and a C-terminal DnaB-binding domain. Belongs to the DnaG primase family. Extended N-terminus.