hRAD17, a structural homolog of the Schizosaccharomyces pombe RAD17 cell cycle checkpoint gene, stimulates p53 accumulation

The RAD17 gene product of S. Pombe is an essential component of the checkpo int control pathway which responds to both DNA damage and disruption of rep lication. We have identified a human cDNA that encodes a polypeptide which is structurally conserved with the S, Pombe Rad17 protein. The human gene, designated hRAD17, predicts an encoded protein of 590 amino acids and a mol ecular weight of 69 kD. Amino acid sequence alignment revealed that hRad17 has 28.3% and 52.5% similarity with the S. Pombe Rad17 protein, and 21.8% i dentity and 45.8% similarity to the budding yeast cell cycle checkpoint pro tein, Rad 24. When introduced into the S. Pombe rad17 mutant, hRAD17 was ab le to partially revert its hydroxyurea and ionizing radiation hypersensitiv ity, but not its UV hypersensitivity. Permanent overexpression of the kRAD1 7 gene in human fibrosarcoma cells resulted in p53 activation and a signifi cant reduction of S- and G2/M-phase cells accompanied by an accumulation of the G1-phase population, suggesting that hRAD17 may have a role in cell cy cle checkpoint control, Immunostaining of HT-1080 cells transiently transfe cted with a hRAD17 construct confirmed the nuclear accumulation of p53, whi ch mimics the induction caused by DNA damage. Using FISH analysis, we have mapped the hRAD17 locus to human chromosome 5q11.2.