The role of the proline-rich region in A1-type myosin essential light chains: Implications for information transmission in the actomyosin complex

The proline-rich region of A1-type myosin essential light chains functions as a spacer arm separating an actin binding site at the extreme N-terminus from the remainder of the protein, Alteration of the length of this region leaving the actin binding site intact results in altered actin-activated MgATPase kinetics when these light chains are hybridised into myosin subfragment-1. In the case of a mutant in which the length of the proline-rich region was doubled, actin binding by the light chain was uncoupled from kinetic modulation. The implications of this result for information transmission in the actomyosin complex are discussed.