A HUMAN HOMOLOG OF THE SCHIZOSACCHAROMYCES-POMBE RAD9(+) CHECKPOINT CONTROL GENE

The product of the Schizosaccharomyces pombe rad9(+) gene is required for cell cycle arrest at the G(2) checkpoints in response to incomplet ely replicated or damaged DNA, We have identified a human cDNA from an infant brain library that is a structural homolog of S. pombe rad9(+) , by searching the dBest data base for sequences similar to the fissio n yeast gene. The human gene encodes a 391-amino acid long, 42,520-Da protein that is approximate to 25% identical and 52% similar to the ye ast protein. The human and yeast gene products demonstrate partial con servation of function, as the human cDNA can rescue to different degre es the sensitivity of S. pombe rad9::ura4(+) cells to the DNA synthesi s inhibitor hydroxyurea and gamma rays, as well as the associated chec kpoint controls, These results suggest an underlying conservation of t he molecular mechanisms of S and G(2) checkpoint control pathways in m ost if not all eukaryotes. Fluorescence ia situ hybridization using a fragment of the corresponding human genome as a probe, in conjunction with PCR reactions employing DNA from human X rodent somatic cell hybr ids, has localized the gene to human chromosome 11q13.1-13.2. This reg ion contains a number of tumor suppressor loci, and based on the biolo gy of checkpoint control genes, HRAD9 should be considered a strong ca ndidate for one of them.