Molecular Biology

Ice Fishing

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Science  19 May 2006:
Vol. 312, Issue 5776, pp. 975
DOI: 10.1126/science.312.5776.975a

Double-stranded DNA is a wonderfully stable repository of information, as can readily be seen in the macroscopic threads of salmon sperm DNA. Compacting and condensing it into higher-order structures such as chromatin and chromosomes protects that information and allows it to fit into the nucleus. Gene expression, however, demands access to unwrapped and unwound DNA strands, which opens the door to unplanned and unwanted double-stranded breaks. These moments of vulnerability touch on a currently debated issue: the relative spatiotemporal distributions of chromosomes, with respect to each other and to transcriptionally active nuclear regions.

Branco and Pombo have adapted fluorescence in situ hybridization for use on ultrathin cryosections and examined how much of each chromosome territory mixes with that of the others (roughly 40% on average). They go on to show that activating expression (by applying interferon-γ to lung fibroblasts) from the MHC class II locus on chromosome 6 increases the penetration of this region into the territories of other chromosomes. Finally, the intriguing correlation between the amount of intermingling in human lymphocytes, calculated for pairs of chromosomes, and previous measurements of translocation frequencies in the same cell type highlights the importance of happenstance in rearrangements. — GJC

PLoS Biol. 4, e138 (2006).

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