FISSION YEAST RAD17 - A HOMOLOG OF BUDDING YEAST RAD24 THAT SHARES REGIONS OF SEQUENCE SIMILARITY WITH DNA-POLYMERASE ACCESSORY PROTEINS

Following DNA damage or a block to DNA synthesis, checkpoint pathways act to arrest mitosis and prevent the attempted segregation of damaged or unreplicated DNA. The rad17 locus of Schizosaccharomyces ces pombe is one of seven known radiation-sensitive (rad) loci which are absolu tely required to prevent mitosis following DNA damage in fission yeast , Six of these (rad1, rad3, rad9, rad17, rad26 and hus1) are also requ ired for the checkpoint which prevents mitosis from occurring before D NA replication is complete. we report here that the predicted rad17 ge ne product is a basic hydrophilic protein of 606 amino acids which con tains five domains with sequence homology to replication factor C (RF- C)/activator 1 subunits. Western analysis and fusion with Green Fluore scent Protein indicate that the abundance and electrophoretic mobility of Rad17 is not significantly modified following a block to DNA synth esis or following DNA damage, and that Rad17 is localized in the nucle us, Rad17 function is not essential for growth, but is required for th e function of the DNA structure-dependent checkpoints, Site-directed m utagenesis has been used to demonstrate the biological significance of the RF-C/activator 1-related domains, These studies have also defined an element of the radiation sensitivity caused by loss of Rad17 funct ion which is not associated with the radiation-induced G(2) arrest def ect seen in the rad17.d null mutant cells.