A LARGE DECREASE IN HEAT-SHOCK-INDUCED PROTEOLYSIS AFTER TRYPTOPHAN STARVATION LEADS TO INCREASED EXPRESSION OF PHAGE-LAMBDA LYSOZYME CLONED IN ESCHERICHIA-COLI

The R gene coding for phage lambda-lysozyme (lambda-L), cloned under the control of the P(L) promoter on a multicopy vector, is expressed in an Escherichia coli strain auxotrophic for tryptophan. Induction by a thermal shift after tryptophan supplementation in a culture initially brought into stationary phase by tryptophan starvation leads to highly increased expression. A thermally unstable mutant protein, difficult to obtain under standard conditions, can be easily produced by post-stationary-phase expression. It is shown that this is due to a drastic decrease in the heat-shock-induced proteolysis normally observed on thermal induction. These data are discussed in relation to our present knowledge of stringent and heat-shock responses.