Mobile origin-licensing factors confer resistance to conflicts with RNA polymerase.

Fundamental to our understanding of chromosome duplication is the idea that replication origins function both as sites where MCM helicases are loaded during the G1 phase and where synthesis begins in S phase. However, the temporal delay between phases exposes the replisome assembly pathway to potential disruption prior to replication. Using multicolor, single-molecule imaging, we systematically study the consequences of encounters between actively transcribing RNA polymerases (RNAPs) and replication initiation intermediates in the context of chromatin. We demonstrate that RNAP can push multiple licensed MCM helicases over long distances with nucleosomes ejected or displaced. Unexpectedly, we observe that MCM helicase loading intermediates also can be repositioned by RNAP and continue origin licensing after encounters with RNAP, providing a web of alternative origin specification pathways. Taken together, our observations reveal a surprising mobility in origin-licensing factors that confers resistance to the complex challenges posed by diverse obstacles encountered on chromosomes. [Display omitted] • RNA polymerase robustly pushes MCMs without slowing down • Nucleosomes are ejected or pushed by MCMs during repositioning • RNA polymerase can bypass ORC or activate ORC sliding and OCCM sliding • Origin licensing continues after RNA polymerase encounters and relocalization Scherr et al. report a single-molecule imaging approach that provides a real-time view of encounters between RNA polymerase and replication origin-licensing factors. They show that origin-licensing factors can be pushed to new locations by RNA polymerase to support alternative origin specification pathways. [ABSTRACT FROM AUTHOR]