Comparative studies of nuclear phosphoproteins from four different muscle tissues and liver

1. Nuclei isolated from red and white skeletal muscle, heart, uterus and liver of rabbit were incubated with [lambda-32P]ATP and the incorporation of 32P into nuclear protein was examined. 2. Liver nuclear proteins were phosphorylated to a much greater extent than those of muscle. Particularly low levels of phosphorylation were observed in white greater extent than those of muscle. Particularly low levels of phosphorylation were observed in white muscle nuclei. 3. Most of the phosphoproteins were common to all the tissues but significant quantitative differences and a limited number of qualitative differences were evident, particularly between liver and the muscle tissues. 4. Many phosphoproteins detected were minor components of the total nuclear protein.