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The Composition of Nuclear RNA of Some Bovine Tissues¹

Department of Pathology, Tulane University School of Medicine, New Orleans, Louisiana

Nuclei previously extracted to remove the acid-soluble and lipid portions, when subjected to hydrolysis in dilute alkali, yielded in addition to the nucleotides expected from the n-RNA,⁴ substances that moved as cations at pH 3.5 and had the absorption spectra characteristic of adenine, guanine, cytosine, and, in the case of thymus nuclei under one set of conditions, uridine. Substances moving very little or not at all in a potential field at pH 3.5 had the spectral characteristics of adenosine and guanine. These substances, called cations for convenience, when added to the nucleotides gave yields and base proportions essentially the same as those of the purines and pyrimidines obtained by subjecting the same supernatant fluid from the alkali hydrolysate to digestion in strong perchloric acid. These cations could not be considered contaminants from the pool of acid-soluble constituents of the cell or to have their origin in any portion of the nuclei other than the nucleoprotein. The finding that n-RNA had one moiety with nucleotide proportions resembling those of microsomal RNA was taken to add support to the theory that n-RNA was a precursor of microsomal RNA. Observations with nuclei extracted with lipid solvents to varying extents suggested the possible association of lipids with a portion of the nucleoprotein that yielded cations in the presence of alkali.

In the nuclei of the 2 normal tissues the proportions of the nucleotides were similar, but the proportions of their cations differed significantly. The lymphosarcoma nuclei had cation proportions markedly different from those of the 2 normal tissues. Among the cations of the normal tissues there was an excess of 6-amino to 6-keto bases by a factor of 3. In the lymphosarcoma the preponderance was by a factor of 15. In both cations and nucleotides, the GC/AU ratios were all relatively close to 1. Thymus nuclei displayed a condition not found in the other nuclei; it was identified by release by dilute alkali of TMP and possibly other compounds yielding thymine on digestion in acid.

¹ This investigation was supported by USPHS Research Grants CA 04969 and CA 08099 from the National Cancer Institute. Preliminary reports on some phases of this work have been presented (13, 14, 17).

⁴ The following abbreviations are used: n-RNA, nuclear RNA; c-RNA, cytoplasmic RNA; A, adenine or its derivative; A₁, a substance with an ultraviolet absorption spectrum characteristie of adenosine; G, guanine or its derivative; G₁, a substance with an absorption spectrum characteristic of guanine; C, cytosine or its derivative; U, uracil or its derivative; U₁, a substance with the absorption spectrum of uridine; TCA, trichloroacetic acid; TMP, thymidylic acid; UMP, uridylic acid; UMP₁, a substance with the absorption spectrum of UMP but with only half the electrophoretic velocity of UMP; AMP, adenylic acid; GMP, guanylic acid; CMP, cytidylic acid.

² American Cancer Society Professor of Experimental Pathology.

³ Present address: 17 Oakdene Drive, Surbiton, Surrey, England.

Received 4/28/65.