The sliding clamp PCNA is a crucial component of the DNA replication machinery. Timely PCNA loading and unloading are central for genome integrity and must be strictly coordinated with other DNA processing steps during replication. Here, we show that the S. cerevisiae Elg1 replication factor C-like complex (Elg1-RLC) unloads PCNA genome-wide following Okazaki fragment ligation. In the absence of Elg1, PCNA is retained on chromosomes in the wake of replication forks, rather than at specific sites. Degradation of the Okazaki fragment ligase Cdc9 leads to PCNA accumulation on chromatin, similar to the accumulation caused by lack of Elg1. We demonstrate that Okazaki fragment ligation is the critical prerequisite for PCNA unloading, since Chlorella virus DNA ligase can substitute for Cdc9 in yeast and simultaneously promotes PCNA unloading. Our results suggest that Elg1-RLC acts as a general PCNA unloader and is dependent upon DNA ligation during chromosome replication.
Bibliographical noteOpen Access funded by Medical Research Council
We thank Dr Anja Bielinsky for plasmids and Dr. M.K. Raghuraman for a cdc9-1 strain. Alexander Lorenz (University of Aberdeen) provided valuable comments on the manuscript. This work was supported by Biotechnology and Biological Sciences Research Council (BBSRC) grant BB/K006304/1 to A.D., Medical Research Council Career Development Fellowship MR/L019698/1 to T.K., and MEXT Grant-in-Aid for Scientific Research on Innovative Areas to K.S.