Figure 1

Nucleotide sequence at the dmsA P1 promoter region and the effects of sequence alterations in the Fnr binding site on dmsA-lacZ expression. The DNA sequence is shown in the middle portion of the figure and is numbered relative to the 5' terminus of the dmsA mRNA (not to scale). The transcriptional start site is located at the guanine residue positioned at 223 bp upstream of the dmsA translational start site and is indicated by the arrow at position +1. The consensus sequence of the RNA polymerase recognition sequences in the -35 and -10 regions are shown below the DNA sequence. The boxed sequences from position -35 to -48 indicate a 14 bp region of dyad symmetry similar to the Fnr consensus recognition sequence (TTGATnnnnATCAA). The location of Fnr-box mutations within the dmsA regulatory region and the corresponding phages carrying the dmsA-lacZ fusions are indicated in the lower portion of the figure. The effect of cis mutations on Fnr-dependent activation of dmsA-lacZ expression is shown in the lower right portion of the figure. β-galactosidase activity was measured from the cells containing the indicated fusion inserted in single copy at the att site. The strains were grown in a buffered LB medium either aerobically or anaerobically. The asterisk represents the fold difference between the fnr^- and fnr⁺ strains.