ATM, the gene mutated in the hereditary disease ataxiaûtelangiectasia, codes for a protein kinase that acts as a master regulator of cellular responses to DNA double-strand breaks. ATM protein is normally inactive and the question of how it becomes active in the event of DNA damage - due to ionizing radiation, for instance - is central to understanding its function.
In this week's Nature (Vol. 421, No. 6922, 30 January 2003, pp. 499-506), Michael B. Kastan and Christopher J. Bakkenist of the St Jude Children's Research Hospital, Memphis, Tennessee, show that the ATM protein is present in normal undamaged cells as an inactive dimer, with its kinase domain bound to a region surrounding serine residue 1981, part of the 'FAT' (focal adhesion target) domain of the protein.
Low doses of ionizing radiation, which induce only a few DNA strand breaks, activate at least half of the total ATM protein present, possibly through a response to changes in chromatin structure, the researchers report.
In an accompanying News and Views article, Jiri Bartek and Jiri Lukas of the Danish Cancer Society, Copenhagen, Denmark, discuss the background and ramifications of this work.
Michael B. Kastan
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