THE 70 KDA SUBUNIT OF REPLICATION PROTEIN-A IS REQUIRED FOR THE G1 S AND INTRA-S DNA-DAMAGE CHECKPOINTS IN BUDDING YEAST/

The rfa1-M2 and rfa1-M4 Saccharomyces cerevisiae mutants, which are al tered in the 70 kDa subunit of replication protein A (RPA) and sensiti ve to UV and methyl methane sulfonate (MMS), have been analyzed for po ssible checkpoint defects. The G1/S and intra-S DNA damage checkpoints are defective in the rfa1-M2 mutant, since rfa1-M2 cells fail to prop erly delay cell cycle progression in response to UV irradiation in G1 and MMS treatment during S phase. Conversely, the G2/M DNA damage chec kpoint and the Smn checkpoint are proficient in rfa1-M2 cells and ail the checkpoints tested are functional in the rfa1-M4 mutant. Preventin g S phase entry by alpha-factor treatment after UV irradiation in G1 d oes not change rfa1-M4 cell lethality, while it allows partial recover y of rfa1-M2 cell viability. Therefore, the hypersensitivity to UV and MMS treatments observed in the rfa1-M4 mutant might only be due to im pairment of RPA function in DNA repair, while the, rfa1-M2 mutation se ems to affect both the DNA repair and checkpoint functions of Rpa70.