BOVINE FAST-TWITCH MYOSIN LIGHT-CHAIN-1 - CLONING AND MESSENGER-RNA AMOUNT IN MUSCLE OF CATTLE TREATED WITH CLENBUTEROL

The cDNA clone encoding the fast-twitch isoform of myosin light chain 1 (MLC-1(f)) from bovine longissimus dorsi muscle and sequenced in M13 and pUC8. An 0.8-kb subclone, produced by digestion of the cDNA with EcoR I, contained the portion of the molecule common to MLC-1(f) and M LC-3(f). The cDNA in pUC8 contained an additional 81 bp upstream of th e EcoR I digestion site, which was unique to MLC-1(f). The cDNA clone was used to measure MLC-1(f) mRNA in longissimus dorsi muscle of cattl e chronically administered the beta-adrenergic agonist clenbuterol. Tr eatment with clenbuterol for 50 days increased succinic dehydrogenase negative (type IIB) and positive (types I and IIA) myofiber cross-sect ional areas by 25%. After the 50-day treatment period, the amount of M LC-1(f) mRNA was 90% greater in longissimus dorsi muscle of treated an imals than in the initial group. This effect was lost when clenbuterol treatment was withdrawn for a 78-day period, during which time muscle growth in the treated animals stopped completely. We conclude that we have cloned the bovine cDNA for MLC-1(f), which has provided addition al evidence that beta-adrenergic agonists increase myofibrillar gene e xpression.