REGULATION OF RNA SYNTHESIS IN ISOLATED NUCLEOLI BY HISTONES AND NUCLEOLAR PROTEINS

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Abstract
Isolated nucleoli from the Novikoff ascites rat tumor were incubated with p32-labeled nucleotides to determine the amount and composition of the RNA (Ribenucleic acid) newly synthesized in-vitro. Addition of calf thymus histone fractions inhibited the synthesis of RNA up to 90%. The composition of the RNA in the presence of added histones was altered in the direction of higher cytidylic plus guanylic acid content. The nucleolar proteins were predominantly HCl-soluble and contained 32% histones. When the nucleoli were pre-treated with trypsin to remove these histones and other HCl-soluble proteins, the composition of the RNA synthesized was shifted in the direction of a lower cytidylic plus guanylic content. The RNA synthesized in the nucleoli stripped of basic proteins approached the composition of DNA (deoryubonucleic acid), while the RNA synthesized in the presence of added histones approached the composition of riboso-mal RNA. The evidence suggests that nucleolar histones are involved in regulation of the "readout" of DNA to produce the RNA characteristic of the ribosomes.