Occasionally, the overall “fit and finish” of DNA is marred by a bubble—a region where complementary DNA strands aren’t complementary at all on account of a sequence of unpaired bases. When a bubble occurs, a protein called XPG rushes to the scene and instigates a repair. But XPG isn’t, as you might think, all about smoothing and polishing. Instead, XPG begins by seemingly making matters worse.
XPG binds bubble DNA and breaks the stacking of unpaired bases, bending DNA severely. Only then does XPG recruit and load into place other proteins that finally smooth things out.