Transcriptional Control of the Nif Regulon in Klebsiella Pneumoniae

Abstract

Expression of the seventeen nitrogen fixation (nif) genes in Klebsiella pneumoniae is regulated in response to both nitrogen source and oxygen tension, so that nitrogenase synthesis is severely repressed by the presence of ammonia, certain amino acids or by dissolved oxygen in the growth medium. Nitrogen control of nif transcription is maintained at two levels; firstly by the ntr system which exerts a general control on nitrogen metabolism and secondly by regulatory proteins encoded by two nif genes, nifA and nifL. The nifA product is required for transcriptional activation of the nif operons (Dixon et al, 1980; Buchanan-Wollaston et al, 1981a) whereas the nifL product has been implicated in repression of nif transcription in response to fixed nitrogen and oxygen (Buchanan-Wollaston et al, 1981b; Hill et al, 1981; Merrick et al, 1982).