Abstract
A clone of a fast isoform of myosin heavy chain (HC) gene was isolated from a cDNAThe sequence data for this cDNA has been submitted to GenBank; the accession number is U03091.
expression library made from mRNA purified from the deep abdominal flexor muscle of the lobster, Homarus americanus. The cDNA (1.5 kb) contained the 3β² untranslated region (UTR) and the coding sequence for the last 413 amino acid residues of the carboxyl terminus of the polypeptide. The deduced amino acid sequence showed high homology with that of myosin HCs from Drosophila (73% identity), nematode (57% identity), and vertebrates (49% identities). Hydropathy plots showed a 28βamino acid periodicity that is consistent with the Ξ±βhelical coiled coil structure of the rod region of native myosin. Northern blot analysis and in situ hybridization showed that the fast myosin HC isoform was expressed only in fast fibers; the probes did not hybridize to mRNA from slow fibers. The message consisted of a single transcript of 6.6 kb. The intracellular localization of the fast myosin mRNA was not uniform. The mRNA was largely confined to the intermyofibrillar spaces and to the subsarcolemmal cytoplasm of the fiber periphery and large infoldings of the cell membrane. Within these regions the mRNA was concentrated in the cytoplasm immediately surrounding the nuclei. This constitutes the first report of the cloning and expression of a myosin HC gene from a crustacean species. Β© 1993 WileyβLiss, Inc.