Characterization of a mammalian smooth muscle myosin heavy chain cDNA clone and its expression in various smooth muscle types.

A cDNA clone, SMHC-29, encoding the light meromyosin of smooth muscle myosin heavy chain (MHC), was isolated from a rabbit uterus cDNA library constructed in phage lambda gt11. This smooth muscle MHC cDNA demonstrates significant nucleotide and amino acid sequence homologies with known sarcomeric MHC genes from rabbit, rat skeletal, and nematode body wall myosin, and even with nonmuscle MHC gene from a slime mold (Dictyostelium discoideum), suggesting that smooth muscle, striated muscle, and nonmuscle MHC genes diverged from a common ancestor. The deduced amino acid sequences of the smooth muscle light meromyosin show very similar periodic distributions of hydrophobic and charged residues as found for the light meromyosin of striated muscle MHCs together with a high potential for alpha-helical formation, indicating an alpha-helical coiled-coil structure for the smooth muscle light meromyosin sequences. Furthermore, S1 nuclease mapping has revealed that this smooth muscle MHC gene for SMHC-29 is specifically expressed in smooth muscles of vascular and nonvascular types but not in the striated muscles or nonmuscle cells.