Cell cycle-dependent TICRR/TRESLIN and MTBP chromatin binding mechanisms and patterns.

BACKGROUND: The selection of replication origins is a defining characteristic of DNA replication in eukaryotes, yet its mechanism in humans has not been well defined. Potential DNA replication origins are licensed through the recruitment of a pair of minichromosome maintenance complexes (MCMs). In yeast, a subset of MCMs is selected for initiation by the SLD3-SLD7 firing factors during G1. Like in yeast, excessive numbers of MCM complexes are loaded onto chromatin during G1 in human cells, but it is unclear how MCMs are selected for firing. RESULTS: We examine genomic binding locations for TICRR/TRESLIN and MTBP, the human orthologs for the yeast replication initiation factors Sld3 and Sld7. TRESLIN and MTBP binding patterns are detectable in a G1 synchronized population and have a higher binding signal compared to asynchronously cycling cells. MTBP binds to early-mid replicating regions in an early S population. Our data suggest MTBP is dependent on TRESLIN for proper association with chromatin during G1 but not S phase. We show that TRESLIN and MTBP binding during G1 does not require origins licensed with loaded MCMs. CONCLUSIONS: We provide evidence for a chromatin binding mechanism of TRESLIN-MTBP during G1 that is dependent on TRESLIN and does not require interactions with licensed origins. MTBP binding location and footprint during S phase differs from that seen in G1, implicating two separate modes of binding. These data highlight binding mechanisms for DNA replication initiation factors in human cells that have diverged from those shown in yeast, suggesting differences in origin selection.