Incorporation of orally administered radioactive precursors into nucleic acids and ribosomes of housefly ovaries

Abstract

After emergence female houseflies were fed for 4 days on a diet containing 14C-orotic acid and 3H-thymidine-5-triphosphate, or 3H-leucine. Nucleic acids and ribosomes were then isolated from the ovaries and studied by MAK column chromatography and sedimentation analysis respectively. The ultraviolet absorption and radioactivity of the fractions were also measured. After MAK column chromatography, the u.v. elution pattern showed that only tow distinct peaks, corresponding to tRNA and rRNA were present. A similar elution pattern was obtained by measuring the 14C from 14C-orotic acid incorporated into the RNA. Because of the small quantity present, DNA was not measurable by u.v. absorption, but by determining the incorporation of 3H from 3H-TTP, its presence was clearly evident. Sedimentation analysis of ovarian ribosomes revealed four polymeric forms besides subunits and monomers. The incorporation of 14C-orotic acid and 3H-leucine into the ribosomes was used to follow the synthesis of rRNA and rProtein respectively. Sucrose density gradient centrifugation of the rRNA indicated that the ovarian rRNA consisted primarily of 28 and 18 S particles.