Regulation of transcription and promoter mapping of the structural genes for nitrogenase (nifHDK) of Azospirillum brasilense Sp7.
Transcription of the structural genes for nitrogenase (nifHDK) in Azospirillum brasilense Sp7 was analysed using Northern blots of total RNA extracted from cultures grown under nitrogen-fixing conditions. Hybridization with an internal nifH probe revealed two transcripts, a major one (by concentration) of 1.1 kb corresponding to nifH and a minor one of 5.6 kb corresponding to nifHDK. Hybridization with nifD or nifK probes revealed the minor transcript of 5.6 kb. This confirms that the nifHDK genes are organized as a single transcription unit and suggests regulation at the level of termination of transcription. The complete nucleotide sequence of nifH was established and the DNA region upstream of the initiation codon was analysed for transcription and translation signals. The nifH open reading frame (ORF) is preceded by an NtrA-dependent promoter and two elements homologous to upstream activator sequences (UAS) required for NifA-mediated activation in other diazotrophs. Promoter mapping with S1 nuclease revealed two start sites located 10 bp and 40 bp downstream of the NtrA-dependent promoter.
de Zamaroczy
M
M
Unité de Physiologie Cellulaire, Institut Pasteur, Paris, France.
Delorme
F
F
Elmerich
C
C
D000595:Amino Acid Sequence; D015806:Azospirillum brasilense / Q000235:genetics*; D001483:Base Sequence; D015152:Blotting, Northern; D005786:Gene Expression Regulation; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012331:RNA, Fungal / Q000235:genetics; D015183:Restriction Mapping; D015719:Single-Strand Specific DNA and RNA Endonucleases
D012331:RNA, Fungal; D015719:Single-Strand Specific DNA and RNA Endonucleases