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CodY Is a Nutritional Repressor of Flagellar Gene Expression in Bacillus subtilis. F. Bergara, 2003.Expression of the  D-dependent
flagellin gene, hag, is repressed by the CodY protein in
nutrient-rich environments . Analysis of a codY mutant bearing
a hag-lacZ reporter suggests that the availability of amino
acids in the environment is the specific signal that triggers this
repression . Further, hag-lacZ expression appears to be
sensitive to intracellular GTP levels, as demonstrated by increased
expression upon addition of decoyinine . This result is consistent
with the postulate that the availability of amino acids in the
environment effects intracellular GTP levels through the stringent
response . However, the levels of hag-lacZ measured upon the
addition of subsets of amino acids suggest an additional
mechanism(s) . CodY is a DNA binding protein that could repress
flagellin expression directly by binding to the hag promoter
region, or indirectly by binding to the fla/che promoter region
that governs expression of the
D
transcriptional activator required for hag gene expression .
Using an electrophoretic mobility shift assay, we have demonstrated
that purified CodY protein binds specifically to both the hag
and fla/che promoter fragments . Additionally, CodY acts as a
nutritional repressor of transcription from the fla/che
promoter region that contains two functional promoters . CodY binds to
both the
D-
and
A-dependent
promoters in this region, as demonstrated by DNase I footprint
analyses . Footprint analyses of the hag gene demonstrated that
CodY binds downstream of its
D-dependent
promoter . Taken together, these results identify new members of the
CodY regulon that encode motility functions in Bacillus subtilis
and are controlled by the
D
alternate sigma factor .
Palindromic Unit-Independent Transposition of IS1397 in Yersinia pestis. Caroline Wilde, 2002.Palindromic units (PUs) are intergenic repeated sequences scattered over the chromosomes of Escherichia coli and several other enterobacteria . In the latter, IS1397, an E . coli insertion sequence specific to PUs, transposes into PUs with sequences close to the E . coli consensus . Reasons for this insertion specificity can relate to either a direct recognition of the target (by its sequence or its structure) by the transposase or an interaction between a specific host protein and the PU target DNA sequence . In this study, we show that for Yersinia pestis, a species deprived of PUs, IS1397 can transpose onto its chromosome, with transpositional hot spots . Our results are in favor of a direct recognition of target DNA by IS1397 transposase . Composition, Acquisition, and Distribution of the Vi Exopolysaccharide-Encoding Salmonella enterica Pathogenicity Island SPI-7. Derek Pickard, 2003.Vi capsular polysaccharide production is encoded by the viaB locus, which has a limited distribution in Salmonella enterica serovars . In S . enterica serovar Typhi, viaB is encoded on a 134-kb pathogenicity island known as SPI-7 that is located between partially duplicated tRNApheU sites . Functional and bioinformatic analysis suggests that SPI-7 has a mosaic structure and may have evolved as a consequence of several independent insertion events . Analysis of viaB-associated DNA in Vi-positive S . enterica serovar Paratyphi C and S . enterica serovar Dublin isolates revealed the presence of similar SPI-7 islands . In S . enterica serovars Paratyphi C and Dublin, the SopE bacteriophage and a 15-kb fragment adjacent to the intact tRNApheU site were absent . In S . enterica serovar Paratyphi C only, a region encoding a type IV pilus involved in the adherence of S . enterica serovar Typhi to host cells was missing . The remainder of the SPI-7 islands investigated exhibited over 99% DNA sequence identity in the three serovars . Of 30 other Salmonella serovars examined, 24 contained no insertions at the equivalent tRNApheU site, 2 had a 3.7-kb insertion, and 4 showed sequence variation at the tRNApheU-phoN junction, which was not analyzed further . Sequence analysis of the SPI-7 region from S . enterica serovar Typhi strain CT18 revealed significant synteny with clusters of genes from a variety of saprophytic bacteria and phytobacteria, including Pseudomonas aeruginosa and Xanthomonas axonopodis pv . citri . This analysis suggested that SPI-7 may be a mobile element, such as a conjugative transposon or an integrated plasmid remnant .
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