Functions of Saccharomyces cerevisiae 14-3-3 Proteins in Response to DNA Damage and to DNA Replication Stress

Two members of the 14-3-3 protein family, involved in key biological processes in different eukaryotes, are encoded by the functionally redundant Saccharomyces cerevisiae BMH1 and BMH2 genes. We produced and characterized 12 independent bmh1 mutant alleles, whose presence in the cell as the sole 14-3-3 source causes hypersensitivity to genotoxic agents, indicating that Bmh proteins are required for proper response to DNA damage. In particular, the bmh1-103 and bmh1-266 mutant alleles cause defects in G1/S and G2/M DNA damage checkpoints, whereas only the G2/M checkpoint is altered by the bmh1-169 and bmh1-221 alleles. Impaired checkpoint responses correlate with the inability to maintain phosphorylated forms of Rad53 and/or Chk1, suggesting that Bmh proteins might regulate phosphorylation/dephosphorylation of these checkpoint kinases. Moreover, several bmh1 bmh2(delta)mutants are defective in resuming DNA replication after transient deoxynucleotide depletion, and all display synthetic effects when also carrying mutations affecting the pol(alpha)-primase and RPA DNA replication complexes, suggesting a role for Bmh proteins in DNA replication stress response. Finally, the bmh1-169 bmh2(delta) and bmh1-170 bmh2 (delta) mutants show increased rates of spontaneous gross chromosomal rearrangements, indicating that Bmh proteins are required to suppress genome instability.