Salt Dissociation of Nuclear Particles Containing DNA-like RNA. Distribution of Phosphorylated and Nonphosphorylated Species

Electrophoresis of proteins from nuclear particles containing DNA-like RNA gave a pattern with 45 bands. The possibility that some of these proteins arose by contamination with ribosomes, chromatin, or soluble nuclear proteins was examined and eliminated. The fate of the proteins of the particles was studied after partial dissociation with 0.25 and 0.70 M NaCl. The individual proteins were released progressively and in different quantities. A group of easily released species (75 and 95% removed with 0.25 and 0.70 M NaCl) was demonstrated. This group contained 8 species between 29,000 and 39,000 daltons which represented approximately one-half of the total number of molecules. It is suggested that they are bound to repetitive sequences of the RNA. At least 30 and 60% of the other proteins were released at 0.25 and 0.70 M NaCl, respectively. There were no specific proteins tightly bound to the RNA, unless the nature of the remaining species is different from that of the released ones of the same molecular weight. The phosphorylated proteins were more tightly bound to the RNA than the nonphosphorylated species of similar molecular weight. In several instances, the 32-P radioactivity was associated with quantitatively minor bands of proteins.