A glimpse of molecular competition

摘要

Chromosomes consist of two interwound DNA strands millions of base pairs in length. These long molecules inevitably suffer breakage, which can be induced by ionizing radiation, biochemicals or natural DNA processing within cells. Double-strand breaks in DNA are not normally lethal to a cell, and can be accurately repaired by a process known as homologous recombination1'2, during which a broken DNA fragment searches for and pairs with an intact strand from another DNA molecule that carries an identical (homologous) sequence. The search process is remarkable in two respects: the homologous partner can be found even among the many millions of non-homologous segments, and the crucial base sequence can be recognized even when it is largely buried within a DNA double helix.