Identification of myosin-binding sites on the actin sequence

The rigor complex of actin and trypsin-treated myosin subfragment 1 (S1) whose heavy chain was cleaved into three fragments (20K, 25K, and 50K) was cross-linked with a zero-length cross-linker, 1-ethyl-3-3-(dimethyl-amino) propylcarbodiimide. The cross-linking reaction generated three types of cross-linked products with apparent molecular weights of 65K, 68K, and 95K. The 65K, 68K, and 95K products were covalently linked complexes of actin-20K fragment of the S1 heavy chain, actin-alkaline light chain 1, and actin-50K fragment of the S1 heavy chain, respectively. Cross-linking sites of S1 heavy and light chains on the actin sequence have been determined by digesting the cross-linked products with cyanogen bromide or with hydroxylamine and then mapping resulting peptides on sodium dodecyl sulfate gels. The result indicates that some of the N-terminal acidic residues of actin at positions 1, 2, 3, 4, and 11 are cross-linking sites of the 20K and 50K fragments of the S1 heavy chain while some of its C-terminal acidic residues at positions 360, 362, and 363 are cross-linking sites of the alkaline light chain 1.