FIG. 2.

fis P sequences and their transcription initiation sites. Each promoter's transcriptional start sites are indicated by arrows that qualitatively depict their relative frequencies of use within each promoter, according to the results in Fig. 1. Only transcripts representing greater than 10% of the total are represented. Nucleotides in bold represent the changes from wild-type E. coli fis P. The numbers at the top indicate the distances from the −10 region (position numbers). Mutations are listed on the left. The bottom two sequences depict the transcription initiation pattern of fis P variants containing mutations outside the initiation region. The −35(16) fis P contains a perfect match to the −35 consensus sequence (TTGACA) positioned 16 bp upstream of the −10 region. The Δ−25G fis P carries a deletion of −25G that shortens the wild-type spacer region from 17 to 16 bp. P.v. is the wild-type fis P from P. vulgaris. As suggested in the text, the arrows in the A₄ promoter may not represent the correct initiation sites. Relative promoter activities are shown on the right. β-Galactosidase assays were performed with RJ1561 cells carrying the respective fis promoters fused to the trp::lacZ in pRJ800. Most of the results have been previously reported (5, 54). The activity of the wild-type (WT) promoter is assigned a value of 1.00, and all other promoter activities are shown relative to this one.