High Molecular Weight Ribonucleic Acids from the Nuclei of Calf Thymus

Abstract

A RIBONUCLEIC acid fraction, which gives the characteristic sedimentation pattern shown in Fig. 1, has been isolated very recently from tobacco leaves¹, mouse brain² and microsomes of rat liver¹. The molecular weights of components A and B are 1.7 × 10⁶ and 0.6 × 10⁶, respectively. Although the study has yet to be extended to other systems, I suggested two years ago that ribonucleic acids with molecular weights of about 1.7 × 10⁶ exist in the cytoplasm of many types of cells³. The question that naturally arises is whether ribonucleic acids of such a molecular weight also exist in a nucleus. So far no investigation along this line has been reported. The results presented below appear to provide an answer to the question.