COMPLETE PRIMARY STRUCTURE OF CHICKEN CARDIAC C-PROTEIN (MYBP-C) AND ITS EXPRESSION IN DEVELOPING STRIATED MUSCLES

C-protein (MyBP-C) is a myosin binding protein of about 140 kDa which is known to modulate myosin assembly in striated muscles. A cardiac-ty pe isoform of C-protein appears not only in cardiac muscle but also in skeletal muscle before skeletal muscle-type isoforms become detectabl e during myogenesis, suggesting that the cardiac isoform is involved i n the early phase of myofibrillogenesis (Bahler et al., 1985; Kawashim a et al., 1986), In this study, in order to understand the structure a nd functional domains of the cardiac-type C-protein, we cloned and seq uenced full-length cDNAs encoding chicken cardiac C-protein from lambd a gt11 cDNA libraries which were prepared with poly (A)(+) RNA from em bryonic chicken cardiac muscle as well as embryonic chicken skeletal m uscle by using antibodies specific for cardiac C-protein. Two cDNA var iants, probably generated by alternative RNA splicing and encoding dif ferent C-protein isoforms, were detected. As judged by the cDNA sequen ces determined, overall homology of the peptide sequence between cardi ac and skeletal muscle C-proteins (Einheber et al., 1990; Furst et al. , 1992, Weber et al., 1994) was about 50-55%. Like other myosin bindin g proteins, skeletal C-proteins, 86 kDa protein and M-protein, cardiac C-protein contains several copies of fibronectin type III motifs and immunoglobulin C2 motifs in the molecule, but their number and arrange ments differed somewhat from those in the other proteins. Northern blo t analysis with the cloned cDNA as a probe demonstrated that mRNA of 5 .0 kb is transcribed in both cardiac and embryonic skeletal muscle, an d that it is specifically expressed in cardiac muscle among adult tiss ues. (C) 1995 Academic Press Limited