RESULTS:
1 - 2 of 2 for ""HI, heterology index""
Filter :
Publication date
Publication
Keyword
Authors
Content type
The role of SOS boxes in enteric bacteriocin regulation
Bacteriocins are a large and functionally diverse family of toxins found in all major lineages of Bacteria. Colicins those bacteriocins produced by Escherichia coli serve as a model system for investigations of bacteriocin structure–function relationships genetic organization and their ecological role and evolutionary history. Colicin expression is often dependent on host regulatory pathways (such as the SOS system) is usually confined to times of stress and results in death of the producing cells. This study investigates the role of the SOS system in mediating this unique form of toxin expression. A comparison of all the sequenced enteric bacteriocin promoters reveals that over 75 % are regulated by dual overlapping SOS boxes which serve to bind two LexA repressor proteins. Furthermore a highly conserved poly-A motif is present in both of the binding sites examined indicating enhanced affinity of the LexA protein for the binding site. The use of gene expression analysis and deletion mutations further demonstrates that these unique LexA cooperative binding regions result in a fine tuning of bacteriocin production limiting it to times of stress. These results suggest that the evolution of dual SOS boxes elegantly accomplishes the task of increasing the amount of toxin produced by a cell while decreasing the rate of uninduced production effectively reducing the cost of colicin production. This hypothesis may explain why such a promoter motif is present at such high frequencies in natural populations of bacteriocin-producing enteric bacteria.
Binding and transcriptional activation of non-flagellar genes by the Escherichia coli flagellar master regulator FlhD2C2
The gene hierarchy directing biogenesis of peritrichous flagella on the surface of Escherichia coli and other enterobacteria is controlled by the heterotetrameric master transcriptional regulator FlhD2C2. To assess the extent to which FlhD2C2 directly activates promoters of a wider regulon a computational screen of the E. coli genome was used to search for gene-proximal DNA sequences similar to the 42–44 bp inverted repeat FlhD2C2 binding consensus. This identified the binding sequences upstream of all eight flagella class II operons and also putative novel FlhD2C2 binding sites in the promoter regions of 39 non-flagellar genes. Nine representative non-flagellar promoter regions were all bound in vitro by active reconstituted FlhD2C2 over the K D range 38–356 nM and of the nine corresponding chromosomal promoter–lacZ fusions those of the four genes b1904 b2446 wzz fepE and gltI showed up to 50-fold dependence on FlhD2C2 in vivo. In comparison four representative flagella class II promoters bound FlhD2C2 in the K D range 12–43 nM and were upregulated in vivo 30- to 990-fold. The FlhD2C2-binding sites of the four regulated non-flagellar genes overlap by 1 or 2 bp the predicted −35 motif of the FlhD2C2-activated σ 70 promoters as is the case with FlhD2C2-dependent class II flagellar promoters. The data indicate a wider FlhD2C2 regulon in which non-flagellar genes are bound and activated directly albeit less strongly by the same mechanism as that regulating the flagella gene hierarchy.