Cloning and characterization of a nonmuscle myosin heavy chain cDNA

Despite many biochemical and structural similarities between muscle and nonmuscle myosins, their genes appear to have completely diverged, since muscle myosin molecular clones will not hybridize to RNA from nonmuscle sources. Here we report the isolation and characterization of a partial myosin heavy chain (MHC) cDNA clone from the slime mold Dictyostelium discoideum. We have isolated this clone from a lambda gt11 expression cDNA library by antibody screening. In contrast to the highly conserved sarcomeric muscle MHC multigene families in other organisms, there appears to be only one gene encoding MHC in the Dictyostelium genome. The cloned portion of this gene does not hybridize to the genomic DNAs of other eukaryotic organisms. Analysis of the predicted amino acid sequence of the partial Dictyostelium MHC clone shows that while there is no sequence homology to known striated muscle MHCs, the structure- and coiled-coil-forming capacities have been conserved.