Fig. 5.
Effect of mutations on the nla28 and nla6 promoter elements. The DNA sequences of the putative σ54 promoters from the nla28 (A) and nla6 (B) operons are shown. Nucleotides within the promoters that were deleted (Δ) or replaced with the indicated bases are shown after the arrowheads. WT and mutant promoters were cloned into a plasmid to create lacZ transcriptional fusions, and strains with the promoter fusion plasmids integrated at the Mx8 phage attachment site in the chromosome were generated. The β-galactosidase–specific activities in cells carrying WT or mutant promoters fused to lacZ were determined at various times in development. The numbers shown after the arrowheads are the relative activities of mutant promoters at the time of peak WT promoter activity.