In summary, a number of different conformational states of F-actin have been described by several different laboratories. Crystal structures have revealed that an opening of the nucleotide-binding cleft, produced by a large rotation of subdomain 2, can occur in G-actin. We have shown that two crystal states of beta-actin, in an open and closed form, can provide a very good model for the conformational difference in F-actin between yeast the wild-type and a V159N mutant. This suggests that some of the dynamics associated with G-actin may provide insights into dynamic processes within the F-actin filament.