Regulation of Azospirillum brasilense nifA gene expression by ammonium andoxygen

The structure and activity of the nifA promoter of Azospirillum brasilense was studied using deletion analysis. An essential region for nifA promoter activity was identified between nucleotides -67 and -47 from the identified transcription start site. A sequence resembling a sigma(70) recognition si te occurs in this region and may constitute the nifA gene promoter. The reg ulation of the nifA gene was studied in plasmid and chromosomal nifA::lacZ fusions. Full expression was obtained under low oxygen levels and in the ab sence of ammonium ions. Repression of nifA expression involves a synergisti c effect between oxygen and ammonium. (C) 1999 Federation of European Micro biological Societies. Published by Elsevier Science B.V. All rights reserve d.