Effect of nifA gene product on expression of lacZ under nifH promoter in Escherichia coli.

Gene expression of the nitrogen fixation system from Klebsiello pneumonice was studied in Escherichia coli by using compatible plasmids as vectors. One constructed plasmid carried the nifH promoter fused to the structural gene for beta-galactosidase, lac Z. Another plasmid carried the promoter of a tetracycline-resistance gene fused to nifA. We found that anaerobic synthesis of beta-galactosidase was greatly enhanced by the presence of an active nifA gene, indicating that its product is a positive control factor for transcription of nifH. In addition, anaerobic expression of lacZ was repressed by ammonium or serine in the presence of nifA. Thus the regulatory mechanism under study is of physiological relevance.