Isolation and purification of RP2-L, a nuclear protein fraction of the Walker 256 carcinosarcoma.

One hour after the injection of 5 fie. of L-lysine-U-C14 into each of a group of rats bearing the Walker 256 carcinosarcoma, the acid-soluble proteins were extracted from nuclear preparations of the tumor. The proteins of these extracts were chromatographed on carboxymethylcellulose, with formic acid as the eluting agent. Rechromatography of 150 mg. of RP2-L1 on carboxymethylcellulose resulted in further purification of the proteins as determined by starch gel electrophoresis, amino acid analysis, N-terminal amino acids, and increase in specific activity. Since lysine comprises 14 per cent of the total amino acid residues, the proteins were classifiable as "slightly lysine-rich" histones. As the proteins were purified, the percentage of N-