RNA metabolism in human celss during amino acid deprivation. I

Abstract

1. 1. Uptake of uridine and incorporation into RNA were concentration dependent. Apparent K m for uridine uptake and incorporation into RNA was for normally growing cells 0.04 mM and for glutamine deficient cells 0.1–0.05 mM. 2. 2. Addition of uridine to the culture medium did not appreciably expand the acid-soluble pool labeled from externally added uridine. 3. 3. Uridine incorporation into RNA attained its maximal rate within a few minutes, at a time when the specific activity of the acid-soluble pool was comparatively low, indicating a compartmentalization of the pool. 4. 4. At saturating concentrations, uridine incorporation into RNA was linear for many hours, indicating a feedback regulation of uridine uptake into the nuclear precursor pool and a preferential reutilization of breakdown products of nuclear turnover RNA. The rate of incorporation into RNA of labeled uridine will therefore be proportional to the accumulation of “stable” species of RNA. 5. 5. Leucine and glutamine deprival gradually decreased RNA accumulation. 6. 6. After the addition of the missing amino acid to prestarved cultures there was a lag priod of about 3 h before any increase in RNA accumulation could be seen. Thus a complete restoration of protein synthesis preceded the increase in RNA accumulation.