Studies of Nuclear Acidic Proteins

Abstract

Abstract Methods are described for the extraction, separation, and electrophoretic analysis of a class of acidic nuclear proteins from various tissues of the rat. Such proteins occur in the chromatin and their distribution in diverse nuclear types is tissue specific. Many of the chromosomal acidic proteins are phosphoproteins which incorporate 32P-orthophosphate in vivo with the formation of phosphoserine and phosphothreonine residues. The patterns of phosphorylation of individual nuclear proteins vary from one tissue to another. Many of the acidic proteins prepared from liver and kidney nuclei of the rat form complexes with rat liver DNA. Binding to the DNA of a closely related species (mouse) also occurs, but to a lesser extent. Little or no binding is observed when rat liver phosphoproteins are added under the same conditions to DNA's from calf thymus, human placenta, dog liver, or bacterial cells (Pneumococcus). Nuclear phosphoproteins stimulate transcription in a cell-free RNA-synthesizing system. Correlations are observed between DNA binding and enhancement of RNA synthesis. DNA-protein complexes have been separated by density gradient centrifugation after annealing has occurred. The nature of the proteins present in the complex depends on the tissue from which the nuclear proteins were isolated.