A key role for replication factor C in DNA replication checkpoint function in fission yeast.

Replication factor C (RF-C) is a five subunit DNA polymerase (Pol) delta/straightepsilon accessory factor required at the replication fork for loading the essential processivity factor PCNA onto the 3'-ends of nascent DNA strands. Here we describe the genetic analysis of the rfc2 +gene of the fission yeast Schizosaccharomyces pombe encoding a structural homologue of the budding yeast Rfc2p and human hRFC37 proteins. Deletion of the rfc2 + gene from the chromosome is lethal but does not result in the checkpoint-dependent cell cycle arrest seen in cells deleted for the gene encoding PCNA or for those genes encoding subunits of either Pol delta or Pol straightepsilon. Instead, rfc2 Delta cells proceed into mitosis with incompletely replicated DNA, indicating that the DNA replication checkpoint is inactive under these conditions. Taken together with recent results, these observations suggest a simple model in which assembly of the RF-C complex onto the 3'-end of the nascent RNA-DNA primer is the last step required for the establishment of a checkpoint-competent state.