Competition for MCM Loading at Origins Establishes Replication Timing Patterns

The MCM helicase is an essential complex that is loaded at origins and designates replication start sites. Along with its biochemical role during S phase, the levels of MCM loaded at specific origins prior to the start of replication have been proposed to contribute to replication timing. In order to probe MCM loading dynamics and their effect on replication timing, we increased and decreased levels of MCM in S. cerevisiae prior to S phase and measured how changes in cellular MCM pools affect genome-wide loading at origins and replication timing.