Peeling back the mystery of DNA overstretching

摘要

When a single DNA molecule is stretched beyond its normal B-form contour length, it will undergo one of two types of conformational transitions at high or low force, depending on its attachment and ability to rotate. The structure of the DNA during these transitions is difficult to measure with traditional structural methods because it only occurs on a single molecule. More than a decade after its discovery, van Mameren et al. (1) have, in this issue of PNAS, directly visualized the mechanics of DNA overstretching for the first time by combining single-molecule force spectroscopy and fluorescence imaging. They show that, regardless of whether or not the molecule can freely rotate, when DNA is stretched to high force it will melt, as the work done by the force to increase the length of the DNA converts double-stranded duplex DNA into ssDNA.