Identification of a new type of mammalian myosin heavy chain by molecular cloning. Overlap of its mRNA with preprotachykinin B mRNA.

In this paper, we report the polypeptide sequence, the mRNA sequence, and gene organization of a new category of mammalian myosin heavy chain, termed myosin I heavy chain-like protein (MIHC), on the basis of sequence analyses of cDNA clones isolated from a bovine intestinal cDNA library and a genomic DNA clone containing the MIHC gene. The MIHC mRNA shares its 3' sequence with the 5' sequence of the preprotachykinin B mRNA encoding the precursor for the neuromedin K neuropeptide. An overlap of these functionally unrelated mRNAs results from overlapping transcription of the same strand of the genomic DNA sequence. The deduced amino acid sequence comprising the amino-terminal two-thirds of the 119-kDa MIHC polypeptide is highly homologous to that portion of conventional myosin heavy chains which forms the globular head domain. The homology is particularly strong in the regions of sequence thought to be involved in forming the nucleotide- and actin-binding sites. By contrast, the deduced sequence comprising the carboxyl-terminal one-third of MIHC shows no significant homology to that portion of conventional myosin heavy chains which forms the alpha-helical coiled-coil rod-like tail. In this regard, MIHC more closely resembles the monomolecular, non-filamentous, low molecular weight myosin I heavy chain from Acanthamoeba castellanii. Furthermore, the size of the MIHC polypeptide, together with its preferential expression in intestinal tissue, leads us to speculate that MIHC and the 110-kDa intestinal brush-border protein (Collins, J. H., and Borysenko, C. W. (1984) J. Biol. Chem. 259, 14128-14135), which binds actin and has myosin-like ATPase activity, are the same or closely related proteins.