Isolation and characterization of cDNA clones encoding the slow myosin alkali light chain

The slow skeletal and cardiac myosin alkali light chains of many different species have identical electrophoretic and immunochemical properties, suggesting that they are encoded by similar or, perhaps, the same mRNAs. In this Thesis, full-length cDNA clones encoding the chicken slow skeletal muscle alkali light chain (MIC), SLC1s,have been isolated and sequenced. These cDNAs have been used to determine whether the mRNAs encoding it and its cardiac counterpart are in fact identical and represented in the genome as a single gene. The analysis of the deduced amino acid sequence of the slow alkali light chain cDNAs showed that there was strong homology with that of other alkali light chains and near identity to a published amino acid sequence of the cardiac isoform. Northern blotting, S1 nuclease protection analyses with probes to either the 5' or 3' regions of the cDNA, and primer extension assays of the 5' region all failed to detect any differences in the mRNAs encoding the adult slow, embryonic, and cardiac alkali myosin light chains. Furthermore, Southern blotting analyses of the chicken genome with probes that reacted with both the slow and cardiac MLC mRNAs showed only a single band of hybridization. The data presented here indicate that, despite their different tissue and temporal patterns of expression, the mRNAs encoding the slow skeletal and cardiac alkali light MLCs are identical and encoded by a single gene.