Figure 5

The T4 primosome is composed of the gp41 hexameric helicase, the gp59 helicase loading protein, the gp61 primase, and the gp32 single stranded DNA binding protein. A.) the gp32 single-stranded DNA binding protein binds to regions of displaced DNA near the replication fork. B.) the bacteriophage T7 gene 4 helicase domain is representative of the hexameric helicases like the T4 gp41 helicase. ATP binding occurs at the interface between domains. C.) the gp59 helicase loading protein recognizes branched DNA substrates and displaces gp32 protein from the lagging strand region adjacent to the fork. Forks of this type are generated by strand invasion during T4 recombination dependent DNA replication. D.) The two domain ATP dependent bacteriophage T7 DNA ligase represents the minimal construct for ligase activity.