HEAT SHOCK-DEPENDENT TRANSCRIPTIONAL ACTIVATION OF THE META GENE OF ESCHERICHIA-COLI

In Escherichia coli, the growth rate at elevated temperatures is contr olled by the availability of endogenous methionine, which is limited b ecause of the temperature sensitivity of the metA gene product, homose rine transsuccinylase (HTS). In order to determine the relationship be tween this control mechanism and the heat shock response, we estimated the cellular levels of HTS during heat shock by Western (immunoblot) analysis and found an increase following induction by temperature shif t and by addition of ethanol or cadmium ions. The elevated level of HT S was a result of transcriptional activation of the metA gene. This ac tivation was heat shock dependent, as it did not take place in rpoH mu tants, and probably specific to the metA gene, as another gene of the methionine regulon (metE) was not activated. These results suggest a m etabolic link between the two systems that control the response of E. coli to elevated temperatures: the metA gene, which codes for the enzy me responsible for regulating cell growth as a function of temperature elevation (HTS), is transcriptionally activated by the heat shock res ponse.