Replication-coupled (RC) nucleosome assembly is an essential process in eukaryotic cells in order to maintain chromatin structure during DNA replication. The deposition of newly synthesized H3/H4 histones during DNA replication is facilitated by specialized histone chaperones. Although the contribution of these histone chaperones to genomic stability has been thoroughly investigated, their effect on replisome progression is much less understood. By exploiting a time-lapse microscopy system for monitoring DNA replication in individual live cells, we examined how mutations in key histone chaperones including CAC1, RTT106, RTT109 and ASF1, affect replication fork progression. Our experiments revealed that mut... More
Replication-coupled (RC) nucleosome assembly is an essential process in eukaryotic cells in order to maintain chromatin structure during DNA replication. The deposition of newly synthesized H3/H4 histones during DNA replication is facilitated by specialized histone chaperones. Although the contribution of these histone chaperones to genomic stability has been thoroughly investigated, their effect on replisome progression is much less understood. By exploiting a time-lapse microscopy system for monitoring DNA replication in individual live cells, we examined how mutations in key histone chaperones including CAC1, RTT106, RTT109 and ASF1, affect replication fork progression. Our experiments revealed that mutations in CAC1 or RTT106 that directly deposit histones on the DNA, slowdown replication fork progression. In contrast, analysis of cells mutated in the intermediary ASF1 or RTT109 histone chaperones revealed that replisome progression is not affected. We found that mutations in histone chaperones including ASF1 and RTT109 lead to extended G2/M duration, elevated number of RPA foci and in some cases, increased spontaneous mutation rate. Our research suggests that histone chaperones have distinct roles in enabling high replisome progression and maintaining genome stability during cell cycle progression.
