gltBDF promoter region. A. Sequence of region upstream of gltB. Nucleotides shown as shaded capitals represent promoter elements or binding sites for the indicated regulatory proteins, as identified in this work and earlier studies (see references in text). The borders shown for binding sites are based on comparison to consensus sequences, and are consistent with DNAse I footprints reported in this study. The binding site for Fnr is shown as a dashed box because it has not been experimentally confirmed (see information on gltBDF at BioCyc.org). The color-shaded background indicates three broad regions of the promoter (initiation region, blue; Lrp-binding region, green; ArgR-binding region, yellow). B. A model for gltBDF transcriptional regulation. Lrp and IHF bind and, according to the model, bend gltBDF promoter DNA such that an upstream regulatory sequence or Lrp surface required for stable binding of RNAP is brought in contact with RNAP that is loosely associated with the promoter region. This positive interaction (and not Lrp binding) is partially abolished by ArgR-Arg bound to glt DNA. In the presence of Crp-cAMP, RNAP association with the promoter is stabilized but in a nonproductive manner, leading to transcriptional repression. Background shading matches that in part A.