Protein kinase activity of Tel1p and Mec1p, two Saccharomyces cerevisiae proteins related to the human ATM protein kinase

The Saccharomyces cerevisiae proteins Tel1p and Mec1p are involved in telom ere length regulation and cellular responses to DNA damage. The closest rel ative of these proteins is the human Ataxia Telangiectasia Mutated (ATM) pr otein, a wortmannin-sensitive protein kinase that primarily phosphorylates serines in an SQ motif. We constructed yeast strains containing functional epitopetagged Versions of Tel1p and Mec1p. We showed that immunoprecipitate d Te[lp and Mec1p were capable of in vitro phosphorylation of the mammalian protein PHAS-1 (Phosphorylated Heat and Acid Stable protein). These activi ties are sensitive to wortmannin. Tel1p phosphorylates serine in an SQ moti f in PHAS-1. Mutations in the kinase domains of Tel1p and Mec1p result in l oss of in vitro kinase activity and the in vivo phenotypes associated with the null tell and mec1 mutations.