Hus1p, a conserved fission yeast checkpoint protein, interacts with Rad1p and is phosphorylated in response to DNA damage

Abstract

The hus1⁺ gene is one of six fission yeast genes, termed the checkpoint rad genes, which are essential for both the S‐M and DNA damage checkpoints. Classical genetics suggests that these genes are required for activation of the PI‐3 kinase‐related (PIK‐R) protein, Rad3p. Using a dominant negative allele of hus1⁺, we have demonstrated a genetic interaction between hus1⁺ and another checkpoint rad gene, rad1⁺. Hus1p and Rad1p form a stable complex in wild‐type fission yeast, and the formation of this complex is dependent on a third checkpoint rad gene, rad9⁺, suggesting that these three proteins may exist in a discrete complex in the absence of checkpoint activation. Hus1p is phosphorylated in response to DNA damage, and this requires rad3⁺ and each of the other checkpoint rad genes. Although there is no gene related to hus1⁺ in the Saccharomyces cerevisiae genome, we have identified closely related mouse and human genes, suggesting that aspects of the checkpoint control mechanism are conserved between fission yeast and higher eukaryotes.