ASPECTS OF CONTROL OF PROTEIN SYNTHESIS IN NORMAL AND REGENERATING RAT LIVER, I. A CYTOPLASMIC RNA-CONTAINING FRACTION THAT STIMULATES AMINO ACID INCORPORATION

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Abstract
Evidence is presented for the occurrence in rat liver cytoplasm of a ribonucleic acid (RNA)-containing fraction having certain properties in common with bacterial messenger RNA. The material stimulates amino acid incorporation in microsomes, is labeled more rapidly in vivo with P32 than are other cytoplasmic RNA fractions, and sediments in a sucrose gradient more rapidly than soluble RNA and more slowly than ribosomes. Preparations of this material from regenerating liver are more active than those from normal liver. Phenol-extracted RNA from the preparation is also active in the in vitro system. It is emphasized, however, that the material appears to differ from bacterial messenger RNA in certain other properties. Notable among these is the insensitivity of the RNA, in the native state, to ribonuclease.