The replisome uses mRNA as a primer after colliding with RNA polymerase

Replication forks are impeded by DNA damage and protein-nucleic acid complexes such as transcribing RNA polymerase. For example, head-on collision of the replisome with RNA polymerase results in replication fork arrest. However, co-directional collision of the replisome with RNA polymerase has little or no effect on fork progression. The current study examines co-directional collisions between a replisome and RNA polymerase in vitro. Surprisingly, we find that the E. coli replisome utilizes the RNA transcript as a primer to continue leading strand synthesis following the collision with RNA polymerase which is displaced from the DNA. This action results in a discontinuity in the leading strand, yet the replisome remains intact and bound to DNA during the entire process. These findings underscore the remarkable plasticity by which the replisome operates to circumvent obstacles in its path and may explain why the leading strand is synthesized discontinuously in vivo.