DETECTION AND CHARACTERIZATION OF MUSCLE-SPECIFIC NUCLEAR PROTEINS

To identify nuclear proteins related to muscle tissue specificity, we tried to prepare antibodies recognizing muscle-specific nuclear protei ns. Taking advantage of the autoimmunity of some nuclear proteins, we prepared an antiserum against chick muscle nuclear proteins by injecti ng protein components of the nuclei isolated from chick breast muscles into breast muscle. Three proteins, named p30, p32, and p37, were det ected with the antiserum in a two-dimensional SDS-PAGE pattern of the isolated nuclei. P30 and p32 were not detected in the nuclei of liver, brain, cardiac muscle, or slow type skeletal muscle (anterior latissi mus dorsi). They were detected in those of fast type skeletal muscle ( pectoralis major and semitendinosus) and smooth muscle (gizzard) at al l developmental stages examined. On serial fractionation of muscle cel l nuclei, they were detected in a fraction obtained after DNase I trea tment of the sample, suggesting that the proteins weakly bind to chrom atin. A homology search of amino acid sequences showed that there is n o known protein similar to p32.