The present study assigns two as yet unidentified fast myosin cDNA clones to specific myosin heavy chain (MHC) isoforms and their mRNAs in different fiber types of rabbit skeletal muscle. Specific oligonucleotide primers were used for reverse transcription and polymerase chain reaction (PCR) to yield products of defined lengths. The method was sensitive enough to detect specific mRNA sequences in total RNA extracts from microdissected, freeze-dried, single-fiber fragments down to 16 ng dry weight. The fibers were typed histochemically and biochemically by their electrophoretically assessed MHC complement. The following results were obtained: clone pMHC20-40 was assigned to type IIB fibers and clone pMHC24-79 to type IID fibers.
