Enhanced activity of the bacteriophage lambda PL promoter at low temperature.

The response of the early phage lambda PL promoter to temperature was investigated. Experiments with lacZ reporter gene fusions demonstrated that the activity of the phage lambda PL promoter is inversely dependent on temperature. The bacterial DNA-binding protein integration host factor (IHF) further enhances lambda PL promoter activity at low temperature, although no apparent changes in the cellular level of IHF protein were observed at the different temperatures. IHF protein binds DNA in vitro more avidly at low temperatures. In vitro transcription assays further revealed that the temperature response of PL is the result of an intrinsic property of the promoter as well as its activation by IHF.