Direct Restart of a Replication Fork Stalled by a Head-On RNA Polymerase

Abstract

When Polymerases Collide Genomes must be replicated by DNA polymerase and copied by RNA polymerase. The two processes occur concurrently in bacteria and, although the majority of bacterial genes are co-oriented with replication, head-on collisions still occur and can result in double-strand breaks in the genome. Pomerantz and O'Donnell (p. 590 ) show, in vitro, that both Escherichia coli DNA and RNA polymerases grind to a halt when they collide bumper to bumper but that the replication fork remains intact, with the RNA polymerase being shunted off the DNA and out of the way. Mfd, a transcription-repair coupling factor, promotes DNA replication restart probably by rewinding separated DNA stands ahead of the halted transcription complex, promoting its displacement from the DNA.