The primase-to-polymerase switch during lagging strand synthesis. (A) DnaB helicase encircles the lagging strand and primase has synthesized a primer. The holoenzyme consists of a dimer of tau that binds two polymerase cores, one gamma complex clamp loader, and two beta clamps. Tau and primase interact with DnaB. Primase must contact SSB to remain on the RNA primer. (B) The chi subunit of gamma complex interacts with SSB, severing the primase-SSB contact and resulting in primase displacement. (C) Primase is then free to synthesize another RNA primer upon contact with DnaB. Diagram (B) also shows that the lagging strand polymerase releases the beta clamp and DNA upon finishing an Okazaki fragment. Diagram (C) shows that after gamma complex assembles the new beta clamp on the upstream primer, the lagging polymerase recruits the new beta clamp (shaded dark) assembled on the upstream RNA primer for the next Okazaki fragment.