Structure and oxygen sensitivity of nifLA promoter of Enterobacter cloacae

The nucleotide sequence of the nifLA promoter of Enterobacter cloacae E26 was determined, and the transcription start site of nifLA was mapped by the primer extension. Studies on the oxygen regulation of E. cloacae nifLA promoter with the nifL'-lacZ fusion showed that the nifLA promoter was sensitive to oxygen as Klebsiella pneumoniae nifLA promoter reported previously. Comparison between the nifLA promoter sequences of E. cloacae and K. pneumoniae revealed the presence of an 11-bp conserved sequence between the -24/-12 consensus of sigma 54-dependent promoter and NtrC binding motif. The 11-bp sequence is speculated to be involved in the oxygen regulation of the nifLA promoter of both enteric bacteria.