Complete primary structure and tissue expression of chicken pectoralis M-protein.

Abstract

Protein (165 kDa) is a structural constituent of myofibrillar "band in striated muscle.We generated a monoclonal antibody which recognized a 165-kDa protein from chicken pectoralis muscle in immunoblot analysis and stained the "band under immunofluorescence microscopy.By screening a Xgtll cDNA library from chicken embryonic pectoralis muscle with this antibody, we isolated a cDNA clone encoding the "protein.Northern blot analysis showed that M-protein mRNA is expressed in pectoralis and cardiac muscle but not in gizzard smooth muscle or non-muscle tissues.Moreover, the anterior latissimus dorsi muscle, which consists almost exclusively of slow fiber types, contains no detectable levels of the mRNA.The fulllength cDNA sequence predicted a 1,450-amino acid polypeptide with a calculated molecular weight of 163 X lo3.The encoded protein contains several copies of two different repetitive motifs: five copies of fibronectin type I11 repeats are in the middle part of the predicted molecule, and two and four copies of the immunoglobulin C2-type repeats are located toward the NHz-terminal and COOH-terminal regions, respectively.This indicates that "protein, along with other thick filament-associated proteins such as C-protein, twichin, and titin, belongs to the superfamily of cytoskeletal proteins with immunoglobulin/fibronectin repeats.