Figure 1.

Structure of the B. japonicum fixRnifA promoter region. (A) Nucleotide sequence of the fixRnifA upstream promoter region, showing the putative NifA binding sites (UAS1, centered at −121, and UAS2, centered at −100), and the protein binding site (PBS) in the −68 region. The overlapping promoter region is also shown (fixRp2/fixRp1). +1 indicates the start of the σ⁵⁴-dependent p1 transcript; +1′ indicates the major transcription start site, p2, for the fixRp2 transcript. (B) Positions presumed to serve as conserved sequences for each promoter. (C) Mutations constructed at the fixRnifA promoter region. Relevant positions for each element are shaded, whereas positions in boxes indicate nucleotide substitutions in the mutant promoters.