Nucleolar specific acidic phosphoprotein C23 is highly methylated.

Protein C23 (Mr = 110,000; pI, 5.5) is the major phosphoprotein in the nucleolus of Novikoff hepatoma cells and comprises 9.5% of the total nucleolar protein. In addition to being highly phosphorylated (1.2 mol % of phosphoserine), it is also highly methylated. Protein C23 contains 1.3 mol % of NG,NG-dimethylarginine and a trace of NG-monomethylarginine.