Novel polymorphism of RecA fibrils revealed by atomic force microscopy.

RecA fibrils in physiological conditions have been successfully imaged using Tapping Mode atomic force microscopy. This represents the first time images of recA have been obtained without drying, freezing and/or exposure to high vacuum conditions. While previously observed structures - the monomer, the hexamer, the short rod - were seen, a new type of fibril was also observed. This protofibril is narrower in diameter than the standard fibril, and occurs in three distinct morphologies: aperiodic, 100-nm periodic, and 150-nm periodic. In addition, much longer rods were observed, and appear curved and even circular.