Complexes of viral and ribosomal ribonucleic acids

Thermal stability of ribosomal ribonucleic acid from baby hamster kidney cells

1. RNA has been prepared from baby hamster kidney cells by extraction with a phenol-EDTA mixture and further purified by passing through a column of Sephadex G-25 that had been equilibrated with water. 2. Aging of the total RNA extracts at 4 degrees or heating at 95 degrees followed by rapid cooling caused a conversion of 28s RNA into material sedimenting in sucrose gradients at approx. 18s. 3. When heated RNA was re-extracted with phenol the sedimentation profile was not returned to that of the unheated RNA. 4. The 28s and 18s RNA fractions were collected separately from sucrose gradients by precipitation with 2vol. of ethanol and passed through a Sephadex G-25 column equilibrated with water. 5. Heat treatment of purified 28s RNA at 95 degrees caused the sedimentation coefficient to increase to approx. 40s, whereas similar treatment of 18s RNA caused no significant increase. If the RNA was heated before the Sephadex G-25 treatment the sedimentation coefficient of the 28s and 18s RNA decreased to approx. 12s and 8s. 6. Heating mixtures of purified 28s and 18s RNA at 95 degrees caused some aggregation of 18s material with the 28s fraction.

Nature of newly synthisized RNA in developing rat brain

Sedimentation characteristics of labelled RNA synthesized in young rat brain slices have been studied by sucrose density gradient centrifugation. A major fraction of the radioactivity derived from adenine-8-C14 in phenol-extractable RNA is shown to be localized in soluble RNA and in relatively small amounts of highly labile fractions in the region lying between 10 S and 20 S. Smaller peaks with S values greater than 30 are also observed. The radioactivity profile of a rapidly labelled RNA isolated from interphase is found to be in sharp contrast with that of phenol-extractable RNA.