Protein synthesis by sheep thyroid extracts

Abstract

Protein synthesis has been demonstrated in the postmitochondrial fraction and in extracts obtained by disruption of particles which sediment between 700 and 20,000 g. The postmitochondrial fraction was maximally active in a reconstituted system of ribosomes and supernatant fraction. Polyuridylic acid specifically stimulated the incorporation of l-phenylalanine into protein, and l-phenylalanyl sRNA was shown to be an intermediate in this reaction. Polyadenylic acid stimulated the incorporation of l-lysine. The system was inhibited by amino acid deprivation, puromycin, and RNase but not by DNase nor actinomycin D. A significant quantity of ribosomes could be isolated from particulate fractions by treatment with deoxycholate. These ribosomes interacted with the postmitochondrial supernatant fraction in protein synthesis. Extracts were prepared by disruption of a particulate fraction sedimenting between 700 and 20,000 g. These extracts responded to synthetic template RNA and could be fractionated into ribosomal and supernatant components. The individual components were inactive alone but could function together or with the complementary postmitochondrial subfraction.