Distinct roles of chromatin-associated proteins MDC1 and 53BP1 in mammalian double-strand break repair

Mol Cell. 2007 Dec 28;28(6):1045-57. doi: 10.1016/j.molcel.2007.12.005.


Phosphorylated histone H2AX ("gamma-H2AX") recruits MDC1, 53BP1, and BRCA1 to chromatin near a double-strand break (DSB) and facilitates efficient repair of the break. It is unclear to what extent gamma-H2AX-associated proteins act in concert and to what extent their functions within gamma-H2AX chromatin are distinct. We addressed this question by comparing the mechanisms of action of MDC1 and 53BP1 in DSB repair (DSBR). We find that MDC1 functions primarily in homologous recombination/sister chromatid recombination, in a manner strictly dependent upon its ability to interact with gamma-H2AX but, unexpectedly, not requiring recruitment of 53BP1 or BRCA1 to gamma-H2AX chromatin. In contrast, 53BP1 functions in XRCC4-dependent nonhomologous end-joining, likely mediated by its interaction with dimethylated lysine 20 of histone H4 but, surprisingly, independent of H2AX. These results suggest a specialized adaptation of the "histone code" in which distinct histone tail-protein interactions promote engagement of distinct DSBR pathways.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing
  • Animals
  • BRCA1 Protein / genetics
  • BRCA1 Protein / metabolism
  • BRCA1 Protein / physiology
  • Blotting, Western
  • Cell Cycle Proteins
  • Cell Line
  • Chromatids / genetics
  • Chromosomal Proteins, Non-Histone
  • DNA Breaks, Double-Stranded*
  • DNA Repair*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • DNA-Binding Proteins / physiology
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • Histones / genetics
  • Histones / metabolism
  • Histones / physiology
  • Humans
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Intracellular Signaling Peptides and Proteins / physiology
  • Mice
  • Microscopy, Fluorescence
  • Mutation
  • Protein Binding / radiation effects
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Recombination, Genetic / radiation effects
  • Transfection
  • Tumor Suppressor p53-Binding Protein 1


  • Adaptor Proteins, Signal Transducing
  • BRCA1 Protein
  • Cell Cycle Proteins
  • Chromosomal Proteins, Non-Histone
  • DNA-Binding Proteins
  • H2AX protein, mouse
  • Histones
  • Intracellular Signaling Peptides and Proteins
  • MDC1 protein, mouse
  • Recombinant Fusion Proteins
  • Trp53bp1 protein, mouse
  • Tumor Suppressor p53-Binding Protein 1
  • XRCC4 protein, mouse
  • Green Fluorescent Proteins