Hybridization with a telomere-specific probe (red) demonstrated that cultures of a human tumor cell line that did not express an inducible NBS1 gene with mutations at sites phosphorylated by the ATM protein had telomeres on the ends of most chromosomes ( purple). In contrast, cultures of this same cell line expressing the inducible mutant NBS1 gene showed a progressive increase in the number of chromosomes without detectable telomeres (not shown), demonstrating that phosphorylation of NBS1 by ATM is important for proper telomere maintenance. For details, see article by Bai et al. on page 1058.

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