TEMPERATURE-MEDIATED REGULATION AND DOWNSTREAM INDUCIBLE SELECTION FOR CONTROLLING GENE-EXPRESSION FROM THE BACTERIOPHAGE-LAMBDA PL PROMOTER

We have examined in detail the effects of various induction temperatures on the expression of a heterologous fusion gene controlled by the bacteriophage λ pL promoter in a heat-inducible Escherichia coli expression system which utilizes the CIts857 repressor. Experiments performed over a temperature range spanning 29-42°C indicate that, under our conditions, temperatures as low as 29°C may be required to fully repress the CI857-controlled transcription from pL, and that the highest protein yields are obtained after induction at 36°C for 6 h. We cloned the cat reporter gene downstream from a heterologous gene controlled by pL and found that cat expression at a low induction temperature permits the monitoring of productive transcription through the heterologous gene and thus aids in selecting transformants that are capable of producing the heterologous protein in E. coli. © 1990.