actin molecule Figure 16-25 Actin filaments. (A) Electron micrographs of negatively stained actin fil minus end minus end aments. (B)Arrangement of actin mole cules in an actin filament, Each filament may be thought of as a two-stranded helix with a twist repeating every 37 nm. Strong interactions between the two strands pre vent the strands from separating, (C)The identical subunits of an actin filament are depicted in different colors to emphasize the close interaction between each actin molecule and its four nearest neighbors (A, courtesy of Roger Craig: C, from K.C. Holmes et al. Nature 347: 44-49, 1990, copyright Macmillan Magazines Ltd 37 nm plus end 50 nm