FIG. 1.

Structure of nifA DNA region from R. leguminosarum bv. viciae UPM791. (A) Gene organization. The grey arrows correspond to genes or open reading frames identified in a 6.9-kb SalI/EcoRI fragment containing the nifA gene from R. leguminosarum and adjacent DNA (EMBL accession no. AJ431175 and AJ520101). The pattern of restriction enzyme cutting sites is indicated below the genetic map. The positions of NifA upstream binding sequences (UAS) and σ⁵⁴-binding sites are indicated by open vertical arrows and grey boxes, respectively. P_ΔnifH and P_nifA1, indicated by horizontal lines below the restriction map, correspond to potential NifA and σ⁵⁴-dependent promoters located upstream of ΔnifH and orf71, respectively. The DNA bordering the NifA region and the cosmids used in its identification are shown at the bottom. (B) Comparison of nucleotide sequences of the region upstream of orf71 plus the 5′ end of orf71 (top line) with the 3′ end of orf5, the intergenic fragment orf5-fixA, and the 5′ end of fixA (bottom line). The numbers on the left indicate the positions of the first nucleotide according to the EMBL accession no. AJ431175 sequence. Nucleotides conserved in both sequences are indicated by asterisks. NifA- and σ⁵⁴-binding sites are enclosed in boxes. The transcription initiation site (+1) of the P_nifA1 promoter is indicated by a vertical arrow.