Defects in the human Artemis protein result in hypersensitivity to DNA double-strand break-inducing agents and the absence of B and T lymphocytes — often referred to as radiosensitive severe combined immune deficiency (RS-SCID) — but the mechanisms underlying these defects remain unclear. In March 22 Cell, Yunmei Ma and colleagues from Norris Comprehensive Cancer Center, Los Angeles, show that the Artemis protein (named after the Greek goddess for the protection of children) cuts away the damaged parts of the DNA so that the strands can be joined together again.

Ma et al. found that purified Artemis protein alone possesses single-strand-specific 5' to 3' exonuclease activity. In addition, Artemis forms a complex with the 469 kDa DNA-dependent protein kinase (DNA-PKcs) in the absence of DNA. DNA-PKcs phosphorylates Artemis, and Artemis acquires endonucleolytic activity on 5' and 3' overhangs, as well as hairpins (Cell 2002, 108:781-794).

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