Small forces like those encountered in living cells can cause measurable, nanometer-scale conformational changes in a four-stranded DNA structure formed during recombination.

Small forces like those encountered in living cells can cause measurable, nanometer-scale conformational changes in a four-stranded DNA structure formed during recombination.

The ability of cells to respond to physical forces is central to development and physiology, but until now it has been difficult to directly measure forces across proteins in vivo. Here, however, a calibrated biosensor is described that can measure forces with high sensitivity across specific proteins in cells. This is applied to the vinculin protein, and a regulatory mechanism is revealed in which the force applied to vinculin determines whether focal adhesions assemble or disassemble.