Electron microscopic observation of monomeric actin attached to a myosin head

Attachment of G-actin to a myosin head was for the first time visualized by electron microscopy of heavy meromyosin (HMM) molecules decorated using a chemical crosslinker with G-actin, which is made resistant to salt- and myosin-induced polymerization by treatment with m-maleimidobenzoic acid N-hydroxysuccinimide ester (MBS). Rotary-shadowed images of acto-HMM molecules crosslinked using MBS or water-soluble carbodiimide showed that MBS-G-actin binds to the distal half of a myosin head (the region 14-15 nm away from the head-rod junction).