Most myosin heavy chain mRNA in L6E9 rat myotubes has a short poly(A) tail.

The mRNA for rat muscle myosin heavy chain (MHC) was isolated from L6E9 myotubes by two rounds of sucrose density gradient centrifugation followed by fractionation on an agarose/polyacrylamide gel. The purity of the mRNA isolated was determined by translation in vitro, peptide analysis of the in vitro product and comparison with authentic MHC, analysis of the kinetics of hybridization with cDNA prepared with this RNA, and titration analysis of total cytoplasmic RNA from muscle and nonmuscle sources. By using the MHC cDNA as probe of myogenic differentiation, it was observed that the level of cytoplasmic MHC mRNA increased approximately 200-fold as the dividing myoblast differentiated into the fused myotube. Titration analysis of RNAs fractionated by oligo(dT)-cellulose chromatography indicated that the majority of the increase occurred in that RNA population that failed to bind to an oligo(dT)-cellulose column.