Comparison of Some Properties of Chromatin Non‐Histone Proteins and Nuclear Sap Proteins

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Abstract
The properties of rat liver and thymus non-histone and nuclear sap proteins were compared. The distribution of total, labile-bound and 0.35 M NaCl extractable non-histone proteins from one organ on polyacrylamide-gel electrophoresis in the presence of sodium dodecylsulfate is quite similar. On electrophoresis non-labeled and 32P-labeled non-histone [NHP] and nuclear sap proteins [NSP] from one organ differ from one another both qualitatively and quantitatively. No appreciable difference was found between non-labeled NPH isolated from liver and thymus. The distribution of 32P-labeled NHP from various organs differs qualitatively rather than quantitatively. Non-labeled and 32P-labeled NSP from liver and thymus differ significantly. ''Free'' NSP and the proteins of ribonucleoprotein [RNP] particles from thymus nuclei contain a great quantity of identical polypeptides; other polypeptides are specific to each of these protein fractions. Upon incubation of nuclei with [.gamma.-32P]ATP the label is incorporated into all the fractions of nuclear protein. The nuclear proteins are phosphorylated at decreasing rates in the order: labile-bound NHP > firmly bound NHP > ''free'' NSP = proteins of RNP particles > histones. NSP and NHP contain protein kinases capable of phosphorylating both these proteins and histones. Histone phosphorylation is sharply inhibited after addition of DNA, the protein kinases of nuclear sap phosphorylating less effectively the histones complexed with DNA than NHP. Both NHP and NSP contain fractions interacting in vitro with DNA. Denatured DNA binds twice as much 32P-labeled NSP and slightly more 32P-labeled NHP than native DNA. Denatured DNA binds NHP and NSP much more effectively than native DNA. It was shown by the membrane filter technique that the major part of the NSP and NHP interacting with native DNA binds to it non-specifically. A certain portion of NHP and NSP interacts specifically with homologous denatured DNA. The possible role of NHP and NSP in the regulation of transcription is discussed.