Cdc45 targeted to lacI repeats (red) leads to decondensation of the chromatin.
Fusion of Cdc45, a protein associated with the replication fork itself, causes widespread decondensation of the chromatin in the system, but Cdc6, a protein required for replication initiation, does not. Moreover, Cdc45 induces phosphorylation of histone H1 by recruiting Cdk2, a protein required for entry into S phase as well as progression through it.
The group did not find evidence of acetylation or methylation changes on the core histones, which have been detected when the same experimental system was used to study transcription-induced chromatin changes. Either such changes are transient during replication—and therefore under the radar of the current experiments—or the mechanisms that underlie chromatin remodeling during replication and transcription differ.