Two identical hydrophobic clusters are present on the same actin monomer: interaction between one myosin subfragment-1 and two actin monomers.

Two-dimensional hydrophobic clusters analysis (HCA) was used to compare the distribution of hydrophobic clusters along various actin sequence. HCA-deduced patterns were not altered by amino-acid variations throughout the evolution of actin and we observed similar hydrophobic motifs comprising myosin subfragment-1 ATP-independent binding sites. HCA suggested the presence of two groups of identical hydrophobic motifs (A1 and A2) which bound on each side of the S1 (63 kDa-31 kDa) connecting segment in relation with two actin monomers. This connection is important in communications between actin- and nucleotide-binding sites. We postulate that some relation and message between the two motifs A1 and A2 take place through myosin subfragment-1 (63 kDa-31 kDa) connecting segment.