Control of Klebsiella pneumoniae nif mRNA synthesis.

Four probes, each specific for a single nif transcript, were used for an analysis of the regulation of nif mRNA synthesis. Transcription of the nifLA operon was repressed by NH4+ but not by amino acids, O2, or temperatures above 37 degrees C. The nifA gene product was required for the activation of transcription of the other nif operons but not nifLA. Synthesis of the other nif transcripts was rapidly turned off by the addition of O2, NH4+, serine, or glutamine. These regulatory effects required the nifL product. However, the nifL product was not required for the cessation of synthesis of these transcripts at elevated temperatures.