COMPONENTS AND DYNAMICS OF DNA-REPLICATION COMPLEXES IN SACCHAROMYCES-CEREVISIAE - REDISTRIBUTION OF MCM PROTEINS AND CDC45P DURING S-PHASE

In S. cerevisiae, the chromatin structure of DNA replication origins c hanges as cells become competent for DNA replication, suggesting that G1 phase-specific association of replication factors with origin DNA r egulates entry into S phase. We demonstrate that ORC, Cdc45p, and MCM proteins are components of prereplication complexes (pre-RC). The MOM- origin association is dependent upon ORC and Cdc6p. During S phase, MC M proteins and Cdc45p dissociate from origin DNA and associate with no norigin DNA with similar kinetics as DNA Polymerase a, which is presen t at DNA replication forks. Our results identify protein components of the pre-RC and a novel replication complex appearing at the G1/S tran sition (the RC), and suggest that after initiation MCM proteins and Cd c45p move with eukaryotic replication forks.