Abstract
Mutants of the RAD9 gene ofSaccharomyces cerevisiae are defective in cell cycle checkpoint arrest in G1 and G2 after treatment with DNA-damaging agents. It is demonstrated that the pronounced G1 arrest observed in yeast after hyperthermia treatment or exposure to paraquat-generated superoxide radicals does not depend on a functional RAD9 gene. For both types of treatments, the mechanism of cell cycle arrest must be considered different from the activation of the DNA damage checkpoint response.