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Two-step activation of ATM by DNA and the Mre11–Rad50–Nbs1 complex


DNA double-strand breaks (DSBs) trigger activation of the ATM protein kinase, which coordinates cell-cycle arrest, DNA repair and apoptosis. We propose that ATM activation by DSBs occurs in two steps. First, dimeric ATM is recruited to damaged DNA and dissociates into monomers. The Mre11–Rad50–Nbs1 complex (MRN) facilitates this process by tethering DNA, thereby increasing the local concentration of damaged DNA. Notably, increasing the concentration of damaged DNA bypasses the requirement for MRN, and ATM monomers generated in the absence of MRN are not phosphorylated on Ser1981. Second, the ATM-binding domain of Nbs1 is required and sufficient to convert unphosphorylated ATM monomers into enzymatically active monomers in the absence of DNA. This model clarifies the mechanism of ATM activation in normal cells and explains the phenotype of cells from patients with ataxia telangiectasia–like disorder and Nijmegen breakage syndrome.

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Figure 1: Dose-dependent activation of ATM by DSBs in the absence of Mre11.
Figure 2: ATM dimer-to-monomer transition can be uncoupled from ATM phosphorylation on Ser1981.
Figure 3: DNA-tethering activity of MRN is required for ATM activation.
Figure 4: ATM is activated by a two-step mechanism in response to DSBs.

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We would like to thank W.G. Dunphy (Caltech) for the complementary DNA encoding ATM protein and T. Paull (University of Texas, Austin) for MRN baculoviruses. We are grateful to R. Baer and the members of Gautier laboratory for their suggestions and critical reading of the manuscript. This work was supported by US National Institutes of Health grant CA 92245 and National Cancer Institute contract N01-CN-25111 to J.G.

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Correspondence to Jean Gautier.

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Supplementary information

Supplementary Fig. 1

Mre11 binding to DNA is independent of H2AX assembly and phosphorylation (PDF 125 kb)

Supplementary Fig. 2

Phosphorylated and unphosphorylated Mre11 binds DNA (PDF 99 kb)

Supplementary Fig. 3

Monomeric and dimeric ATM binds DNA (PDF 61 kb)

Supplementary Fig. 4

Characterization of recombinant MRN complexes (PDF 114 kb)

Supplementary Fig. 5

Limit of detection of DNA purified from extracts (PDF 258 kb)

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Dupré, A., Boyer-Chatenet, L. & Gautier, J. Two-step activation of ATM by DNA and the Mre11–Rad50–Nbs1 complex. Nat Struct Mol Biol 13, 451–457 (2006).

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