THE ATR AND ATM PROTEIN-KINASES ASSOCIATE WITH DIFFERENT SITES ALONG MEIOTICALLY PAIRING CHROMOSOMES

A number of cell-cycle checkpoint genes have been shown to play import ant roles in meiosis. We have characterized the human and mouse counte rpart of the Schizosaccharomyces pombe Rad3 protein, named Atr (for at axia-telangiectasia- and rad3-related), and the protein that is mutate d in ataxia-telangiectasia, Atm. We demonstrate that ATR mRNA and prot ein are expressed in human and mouse testis. More detailed analysis of specific cells in seminiferous tubules shows localization of Atr to t he nuclei of cells in the process of meiosis I. Using immunoprecipitat ion and immunoblot analysis, we show that Atr and Atm proteins are sim ilar to 300 and 350 kD relative molecular mass, respectively, and furt her demonstrate that both proteins have associated protein kinase acti vity. further, we demonstrate that Atr and Atm interact directly with meiotic chromosomes and show complementary localization patterns on sy napsing chromosomes. Atr is found at sites along unpaired or asynapsed chromosomal axes, whereas Atm is found along synapsed chromosomal axe s. This is the first demonstration of a nuclear association of Atr and Atm proteins with meiotic chromosomes and suggests a direct role for these proteins in recognizing and responding to DNA strand interruptio ns that occur during meiotic recombination.