Figure 4. Models of auxiliary helicase activity in promoting replication through transcription complexes. (A) Dda helicase acts on the lagging strand to promote progression of the core T4 replisome through a co-directional RNAP in vitro. (B) UvrD helicase acts on the leading strand to promote replication through a Tus-Ter termination complex. (C) DinG acts on the lagging strand in collaboration with either UvrD or Rep on the lagging strand to promote replication through head-on transcription complexes. (D) Rep or UvrD act on the leading strand opposite DnaB to promote replication through a mutant EcoRI protein block.