The AraC/XylS Protein MxiE and Its Coregulator IpgC Control a Negative Feedback Loop in the Transcriptional Cascade That Regulates Type III Secretion in Shigella flexneri.

Members of the AraC family of transcriptional regulators (AFTRs) control the expression of many genes important to cellular processes, including virulence. In species, the type III secretion system (T3SS), a key determinant for host cell invasion, is regulated by the three-tiered VirF/VirB/MxiE transcriptional cascade. Both VirF and MxiE belong to the AFTRs and are characterized as positive transcriptional regulators.

Investigating the DNA-Binding Site for VirB, a Key Transcriptional Regulator of Virulence Genes, Using an In Vivo Binding Tool.

The transcriptional anti-silencing and DNA-binding protein, VirB, is essential for the virulence of species and, yet, sequences required for VirB-DNA binding are poorly understood. While a 7-8 bp VirB-binding site has been proposed, it was derived from studies at a single VirB-dependent promoter, . Our previous in vivo studies at a different VirB-dependent promoter, , found that the proposed VirB-binding site was insufficient for regulation.

Insights into transcriptional silencing and anti-silencing in Shigella flexneri: a detailed molecular analysis of the icsP virulence locus.

Transcriptional silencing and anti-silencing mechanisms modulate bacterial physiology and virulence in many human pathogens. In Shigella species, many virulence plasmid genes are silenced by the histone-like nucleoid structuring protein H-NS and anti-silenced by the virulence gene regulator VirB. Despite the key role that these regulatory proteins play in Shigella virulence, their mechanisms of transcriptional control remain poorly understood.

Characterization of SlyA in Shigella flexneri Identifies a Novel Role in Virulence.

The SlyA transcriptional regulator has important roles in the virulence and pathogenesis of several members of the Enterobacteriaceae family, including Salmonella enterica serovar Typhimurium and Escherichia coli. Despite the identification of the slyA gene in Shigella flexneri nearly 2 decades ago, as well as the significant conservation of SlyA among enteric bacteria, the role of SlyA in Shigella remains unknown. The genes regulated by SlyA in closely related organisms often are absent from or mutated inS.

The CpxR/CpxA two-component regulatory system up-regulates the multidrug resistance cascade to facilitate Escherichia coli resistance to a model antimicrobial peptide.

A genome-wide susceptibility assay was used to identify specific CpxR-dependent genes that facilitate Escherichia coli resistance to a model cationic antimicrobial peptide, protamine. A total of 115 strains from the Keio Collection, each of which contained a deletion at a demonstrated or predicted CpxR/CpxA-dependent locus, were tested for protamine susceptibility. One strain that exhibited high susceptibility carried a deletion of tolC, a gene that encodes the outer membrane component of multiple tripartite multidrug transporters.

Mg2+ facilitates leader peptide translation to induce riboswitch-mediated transcription termination.

We have characterized a 17-residue peptide, MgtL, which is translated specifically in high Mg(2+) from an open reading frame (ORF) embedded in the Mg(2+) riboswitch domain, previously identified in the 5' leader region of Mg(2+) transporter gene mgtA in Salmonella. We demonstrate that mgtL translation is required to prematurely terminate mgtA transcription. Abrogation of mgtL translation by mutation of its start codon results in transcription of the mgtA-coding region in high Mg(2+), suggesting that ribosome stalling is not required for preventing premature transcription termination.

The CpxR/CpxA two-component system up-regulates two Tat-dependent peptidoglycan amidases to confer bacterial resistance to antimicrobial peptide.

We demonstrate that the twin arginine translocation (Tat) system contributes to bacterial resistance to cationic antimicrobial peptides (CAMPs). Our results show that a deletion at the tatC gene, which encodes a subunit of the Tat complex, caused Salmonella and Escherichia coli to become susceptible to protamine. We screened chromosomal loci that encode known and predicted Tat-dependent proteins and found that two N-acetylmuramoyl-l-alanine amidases, encoded by amiA and amiC, elevated bacterial resistance to protamine and α-helical peptides magainin 2 and melittin but not to β-sheet defensin HNP-1 and lipopeptide polymyxin B.