Acanthamoeba myosin IA, IB, and II heavy chains are synthesized in vitro from Acanthamoeba messenger RNA.

Addition of a myosin IB polyclonal antibody, which reacts with the heavy chains of both myosins IA and IB, to the [35S]methionine-labeled proteins synthesized in vitro using Acanthamoeba messenger RNA specifically immunoprecipitated radioactive polypeptides that migrated on sodium dodecyl sulfate-polyacrylamide gels exactly with the heavy chains of purified myosins IA and IB. A myosin II polyclonal antibody specifically immunoprecipitated a radioactive polypeptide which migrated exactly with the heavy chain of myosin II. These results provide strong evidence that Acanthamoeba myosins IA, IB, and II are separate gene products and that the purified proteins contain native, undegraded heavy chains. These results are especially important for myosins IA and IB, because they possess unusually small heavy chains for myosins.