SOME ASPECTS OF RIBONUCLEIC ACID SYNTHESIS IN ISOLATED CELL NUCLEI

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Abstract
The metabolic "heterogeneity" of RNA in the thymus nucleus has been reported previously. The present report describes a method of fractionation of nuclear ribonucleic acids and its application to tracer studies of RNA synthesis in the isolated nucleus. The results offer a convincing illustration of the complexity of nuclear RNA and demonstrate the separate and widely divergent metabolic activities of 2 different ribonucleic acid fractions. Of 2 distinct fractions of the ribonucleic acids of isolated thymus nuclei, one probably represents ribonucleic acid of the nucleolus. Studies of the incorporation of orotic acid-6-C14 and adenosine-8-C14 into these RNA fractions in vitro show great differences in their metabolic activity and different susceptibilities to an inhibitor of RNA synthesis, the "nucleolar" RNA being by far the more active.