ATP-dependent DNA helicase essential for viral DNA replication and recombination (PubMed:10871615). The helicase moves 5' -> 3' on the lagging strand template, unwinding the DNA duplex ahead of the leading strand polymerase at the replication fork and generating ssDNA for both leading and lagging strand synthesis (PubMed:11459969, PubMed:23578280). Interaction with the primase allows the primase to initiate lagging strand synthesis and fully activates the helicase (PubMed:22869700, PubMed:23578280). Loaded by the helicase assembly factor on replication forks that begin at discrete replication origin sequences, as well as on forks that are created during recombination (PubMed:10871615). Homohexamer (PubMed:7706292, PubMed:22869700, PubMed:23578280). The homohexamer is a trimer of asymmetric dimers (PubMed:7706292). Interacts with the DNA primase; this interaction forms the active primosome complex, which is composed of 6 helicase and 1 primase subunits and expresses full helicase and primase activities (PubMed:22869700, PubMed:23578280). Interacts (via C-terminus) with the helicase assembly factor; this interaction brings about the rapid assembly of the helicase onto ssDNA (PubMed:7806533, PubMed:10871615). Part of the replicase complex that includes the DNA polymerase, the polymerase clamp, the clamp loader complex, the single-stranded DNA binding protein, the primase, the DnaB-like replicative helicase and the helicase assembly factor (PubMed:16800624). Belongs to the helicase family. DnaB subfamily.