Yeast Genetics and Molecular Biology 2000
University of Washington
Seattle, Washington USA
July 2000

Name: Bashkirov, Vladimir
Mailing Address: Section of Microbiology, University of California, One Shields Ave., Davis, CA 95616, USA
Email Address: vibashkirov@ucdavis.edu
Phone & FAX numbers: (530)7523016 & (530)7523011

#059

Rad55 protein phosphorylation links DNA damage checkpoints and recombinational DNA repair.
Vladimir Bashkirov, Elena Bashkirova, Edwin Haghnazari, Alan Chan, Wolf-Dietrich Heyer
Section of Microbiology, University of California, One Shields Ave., Davis, CA 95616, USA

The response to DNA damage is manifested by transient cell cycle arrest and by changes in the transcriptional pattern of the cells, both of which are regulated by the checkpoint system. Multiple DNA repair mechanisms ensure cell survival and genomic stability. We show that the two systems, checkpoint control and DNA repair, are intrinsically linked in S.cerevisiae through the post-translational modification of the recombinational DNA repair protein Rad55. Rad55p was phosphorylated in response to DNA damage induced by methyl methansulfonate, UV and gamma rays, and replication block induced by hydroxyurea. Rad55p phosphorylation does not occur during a normal cell cycle in the absence of DNA damage. Mutations in the central checkpoint kinases, MEC1, RAD53 and DUN1, abolished or severely affected Rad55p phosphorylation. The cell cycle arrest and transcriptional response to DNA damage was found to be intact in rad55 deletion strain. Rad55p was phosphorylated only in a context of a stable heterodimer with Rad57p. We conclude that the double-strand break repair protein Rad55 is a terminal substrate of DNA damage and replication block checkpoints. A strong defect in DNA damage-induced mitotic recombination was found in checkpoint-deficient mec1 cells, which was not suppressed by an artificial cell cycle arrest. We propose a model in which DNA damage checkpoints modulate the activity of the recombinational repair pathway by direct phosphorylation of the Rad55 protein.

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