Studies on the amino acid regulation of RNA-synthesis in mammalian cells in tissue culture

Abstract

In normal stringent control of RNA synthesis in bacteria, RNA formation is dependent on the internal concentration of amino acids in the cells. To find out if mammalian cells have a similar regulatory link between the availability of amino acids for protein synthesis and RNA formation, was the aim of the present investigation. RNA, protein and DNA synthesis was studied in monolayer cultures of mouse fibroblasts (strain L-929). Macromolecular synthesis was measured by the incorporation of 14C-uridine and radioactive amino acids respectively, into acid-insoluble product. Amino acid starvation was achieved by excluding all free amino acids and serum from the medium. Serum starvation for up to 12 h was found not to diminish DNA or protein synthesis. RNA synthesis was depressed to 20–50%. The rate of RNA synthesis in mouse fibroblasts was unimpaired under conditions where the rate of protein synthesis was decreased to 30% of normal by amino acid starvation. This protein synthesis in the absence of added amino acids was shown to be related to the rate of intracellular protein degradation. The uptake of 14C-uridine into the uridine nucleotide pools of the cells was similarly unimpaired by amino acid starvation. In contrast, DNA synthesis was markedly inhibited by amino acid starvation. The DNA synthesis of starved cells diminished gradually and seemed to stop after 4 to 6 h of starvation. This time period is comparable to the length of the DNA-synthesis period (S-phase) of this strain of fibroblasts.