THE ANAPHASE INHIBITOR OF SACCHAROMYCES-CEREVISIAE PDS1P IS A TARGET OF THE DNA-DAMAGE CHECKPOINT PATHWAY

Inhibition of DNA replication and physical DNA damage induce checkpoin t responses that arrest cell cycle progression at two different stages . In Saccharomyces cerevisiae, the execution of both checkpoint respon ses requires the Mec1 and Rad53 proteins. This observation led to the suggestion that these checkpoint responses are mediated through a comm on signal transduction pathway. However, because the checkpoint-induce d arrests occur at different cell cycle stages, the downstream effecte rs mediating these arrests are likely to be distinct. We have previous ly shown that the S. cerevisiae protein Pds1p is an anaphase inhibitor and is essential for cell cycle arrest in mitosis in the presence DNA damage. Herein we show that DNA damage, but not inhibition of DNA rep lication, induces the phosphorylation of Pds1p. Analyses of Pds1p phos phorylation in different checkpoint mutants reveal that in the presenc e of DNA damage, Pds1p is phosphorylated in a Mec1p- and Rad9p-depende nt but Rad53p-independent manner. Our data place Pds1p and Rad53p on p arallel branches of the DNA damage checkpoint pathway. We suggest that Pds1p is a downstream target of the DNA damage checkpoint pathway and that it is involved in implementing the DNA damage checkpoint arrest specifically in mitosis.