RepB_primase is a DNA-primase produced by P4-like phages. It is a zinc-independent primase unlike Pri-type primases. It takes up a dumbbell shaped consisting of an N-terminal catalytic domain separated by a long alpha-helix plus tether and a C-terminal helical-bundle domain. Primases are necessary for phage replication. RepBprime primases such as in this family recognize both ssiA and ssiB, ie only 1 single-stranded primase initiation site on each strand, independently of each other and then synthesize primers that are elongated by DNA polymerase III. The phage is thus replicated exclusively in leading strand mode.