What happens when replication and transcription complexes collide?

The arrest of replication forks due to collisions with transcription complexes leads to genomic instability and cell death. Mechanisms that promote the progression of replication forks past transcription complexes are therefore essential for propagation and preservation of the genome. Recent studies of E. coli directly investigate the consequences of collisions of the replisome with RNAP polymerase (RNAP) in vitro and provide novel mechanisms by which these encounters may be resolved. Additionally, recent in vivo and in vitro studies support the longstanding hypothesis that auxiliary DNA helicases promote replication through roadblocks such as transcription complexes. Here we review past and recent advances that formulate our current understanding of how the bacterial replisome deals with transcription complexes along the path of chromosome duplication.