SYNTHESIS OF A SPECIFIC MESSENGER RNA DURING AMINO ACID STARVATION OF ESCHERCHIA COLI

Messenger RNA regulation in Escherichia coli has been examined during tryptophan starvation by measuring specific protein and messenger RNA synthesis in an isogenic pair of tryptophan auxotrophs possessing either the stringent or relaxed allele of the RC locus. The formation of the tryptophan synthetase A and B proteins following derepression of the tryptophan operon in these strains was found to be higher in the tryptophan starved stringent strain than in the relaxed strain. This suggested that tryptophan messenger RNA is synthesized at a high rate during starvation even though over-all RNA synthesis is reduced by 80 to 90%. By pulse-labeling RNA during derepression of the tryptophan operon, we have measured the fraction of the labeled RNA which can be characterized as tryptophan messenger RNA by hybridization to φ80 phage DNA which has incorporated all or part of the tryptophan operon into its genome. After more than one hour of tryptophan starvation, the fraction of pulse-labeled RNA which is tryptophan messenger RNA is ten times as great in the stringent strain as in the relaxed strain. We conclude that RNA regulation during amino acid starvation is not co-ordinate and that the effects of the RC locus pertain to regulation of ribosomal and transfer RNA. From the hybridization data it is estimated that the steady-state number of tryptophan messenger RNA molecules per bacterium during derepression of the tryptophan operon is about seven molecules. © 1968.