Role of Dot1-Dependent Histone H3 Methylation in G₁ and S Phase DNA Damage Checkpoint Functions of Rad9

Abstract

We screened radiation-sensitive yeast mutants for DNA damage checkpoint defects and identified Dot1, the conserved histone H3 Lys 79 methyltransferase. DOT1 deletion mutants (dot1Δ) are G₁ and intra-S phase checkpoint defective after ionizing radiation but remain competent for G₂/M arrest. Mutations that affect Dot1 function such as Rad6-Bre1/Paf1 pathway gene deletions or mutation of H2B Lys 123 or H3 Lys 79 share dot1Δ checkpoint defects. Whereas dot1Δ alone confers minimal DNA damage sensitivity, combining dot1Δ with histone methyltransferase mutations set1Δ and set2Δ markedly enhances lethality. Interestingly, set1Δ and set2Δ mutants remain G₁ checkpoint competent, but set1Δ displays a mild S phase checkpoint defect. In human cells, H3 Lys 79 methylation by hDOT1L likely mediates recruitment of the signaling protein 53BP1 via its paired tudor domains to double-strand breaks (DSBs). Consistent with this paradigm, loss of Dot1 prevents activation of the yeast 53BP1 ortholog Rad9 or Chk2 homolog Rad53 and decreases binding of Rad9 to DSBs after DNA damage. Mutation of Rad9 to alter tudor domain binding to methylated Lys 79 phenocopies the dot1Δ checkpoint defect and blocks Rad53 phosphorylation. These results indicate a key role for chromatin and methylation of histone H3 Lys 79 in yeast DNA damage signaling.

ACKNOWLEDGMENTS

We thank C. D. Allis, J. Downs, D. E. Gottschling, J. Haber, D. Lydall, M. A. Osley, D. F. Stern, K. Struhl, and Y. Zhang for generously sharing strains, reagents, methods, and unpublished data.

This study was supported by grants from the NIH (R01 GM60443) and Ludwig Fund for Cancer Research to S.J.K. and the CIHR to J.C. A.J. is supported by the University of Chicago MSTP and an AHA Greater Midwest predoctoral fellowship. J.C. is a CIHR Investigator, and S.J.K. is a Leukemia and Lymphoma Society Scholar.