THE SACCHAROMYCES-CEREVISIAE MEC1 GENE, WHICH ENCODES A HOMOLOG OF THE HUMAN ATM GENE-PRODUCT, IS REQUIRED FOR G(1) ARREST FOLLOWING RADIATION TREATMENT

The Saccharomyces cerevisiae gene MEC1 represents a structural homolog of the human gene ATM mutated in ataxia telangiectasia patients, Like human ataxia telangiectasia cell lines, mec1 mutants are defective in G(2) and S-phase cell cycle checkpoints in response to radiation trea tment. Here we show an additional defect in G(1) arrest following trea tment with UV light or gamma rays and map a defective arrest stage at or upstream of START in the yeast cell cycle.