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Single-stranded DNA-binding protein hSSB1 is critical for genomic stability


Single-strand DNA (ssDNA)-binding proteins (SSBs) are ubiquitous and essential for a wide variety of DNA metabolic processes, including DNA replication, recombination, DNA damage detection and repair1. SSBs have multiple roles in binding and sequestering ssDNA, detecting DNA damage, stimulating nucleases, helicases and strand-exchange proteins, activating transcription and mediating protein–protein interactions. In eukaryotes, the major SSB, replication protein A (RPA), is a heterotrimer1. Here we describe a second human SSB (hSSB1), with a domain organization closer to the archaeal SSB than to RPA. Ataxia telangiectasia mutated (ATM) kinase phosphorylates hSSB1 in response to DNA double-strand breaks (DSBs). This phosphorylation event is required for DNA damage-induced stabilization of hSSB1. Upon induction of DNA damage, hSSB1 accumulates in the nucleus and forms distinct foci independent of cell-cycle phase. These foci co-localize with other known repair proteins. In contrast to RPA, hSSB1 does not localize to replication foci in S-phase cells and hSSB1 deficiency does not influence S-phase progression. Depletion of hSSB1 abrogates the cellular response to DSBs, including activation of ATM and phosphorylation of ATM targets after ionizing radiation. Cells deficient in hSSB1 exhibit increased radiosensitivity, defective checkpoint activation and enhanced genomic instability coupled with a diminished capacity for DNA repair. These findings establish that hSSB1 influences diverse endpoints in the cellular DNA damage response.

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Figure 1: ATM-dependent stabilization and phosphorylation of hSSB1 after ionizing radiation.
Figure 2: hSSB1 localizes to DNA repair foci after ionizing radiation.
Figure 3: hSSB1 inhibition results in defective ionizing-radiation-induced checkpoint activation and defective ATM signalling.
Figure 4: hSSB1 is required for efficient DNA repair.

Accession codes

Primary accessions

Gene Expression Omnibus

Data deposits

The genes hSSB1 and hSSB2 are deposited in NCBI under accession numbers NM_024068 and NM_001031716, respectively.


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This study was supported by grants from the National Health and Medical Research Council of Australia (to K.K.K.), Cancer Research UK (to S.C.W.), the Biotechnology and Biological Sciences Research Council of the UK (to M.F.W), the National Institutes of Health (CA92245 to J.G.; CA10445 and CA123232 to T.K.P.) and the American Cancer Society (RGS-04-173-01-CCG to T.T.P.).

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Correspondence to Malcolm F. White or Kum Kum Khanna.

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Richard, D., Bolderson, E., Cubeddu, L. et al. Single-stranded DNA-binding protein hSSB1 is critical for genomic stability. Nature 453, 677–681 (2008).

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