Polymerization of mutant actins at different temperatures. WT, G156S, G156D, and G268D actins were incubated in F-buffer at 4, 15, 25, and 37 °C and ultracentrifuged. The resulting supernatant and pellet fractions were subjected to SDS-PAGE and quantified (A). B, electron micrographs of G156D, G156S, and G268D actins incubated in F-buffer at 4 or 37 °C. Scale bar, 100 nm.