Crystalline actin tubes. IV. Structural information on actin monomers obtained from computer-averaged lattice images.

Crystalline actin tubes can be formed in the presence of Pr(III) and examples can be selected which are opened along their length. The structural unit cell seen in electron micrographs were computer-averaged to obtain the projected size and shape of the actin monomer. There are two monomers per unit cell, each related by a two-fold axis perpendicular to the plane of the projection. Each 3.3 x 5.5 nm monomer was markedly asymmetric. Skeletal muscle actin strongly resembles Acanthamoeba actin (Aebi et al. (1980) Nature 288, 296) although the projected dimensions may vary slightly.