A NOVEL TYPE OF MYOSIN IMPLICATED IN SIGNALING BY RHO-FAMILY GTPASES

A novel widely expressed type of myosin (fifth unconventional myosin f rom rat: myr 5) from rat tissues, defining a ninth class of myosins, w as identified, The predicted amino acid sequence of myr 5 exhibits sev eral features not found previously in myosins. The myosin head domain contains a unique N-terminal extension and an insertion of 120 amino a cids at a postulated myosin-actin contact site, Nevertheless, myr 5 is able to bind actin filaments in an ATP-regulated manner, The head dom ain is followed by four putative light chain binding sites. The tail d omain of myr 5 contains a region which coordinates two atoms of zinc f ollowed by a region that stimulates GTP hydrolysis of members of the r as-related rho subfamily of small G-proteins. Myr 5 therefore provides the first direct link between rho GTPases which have been implicated in the regulation of actin organization and the actin cytoskeleton, It is also the first unconventional myosin for which a tail binding part ner(s), namely members of the rho family, has been identified.