Using global transcriptome and promoter activation analysis, we have shown that the BsaN regulon occupies a central position in modulating the expression of T3SS3, T6SS1 and several additional loci that are likely involved in promoting HSP phosphorylation Virulence and intracellular Selonsertib solubility dmso survival. Regulatory factors may act to control expression by acting directly on a given gene, or indirectly by modulating a regulatory intermediate. We found that BsaN in complex with the T3SS3 chaperone BicA directly controls the expression of 19 loci in a region
of chromosome 2 containing T6SS1 and T3SS3 accessory genes (BPSS1494-BPSS1533). BsaN/BicA activated transcription of the operons encoding T3SS3 effector proteins, the BipBCD translocon complex, chaperones, and other transcriptional regulators, as well as two genes of unknown function (BPSS1513-1514). BsaN/BicA upregulates expression of T6SS1 by activating the transcription of the two component regulatory system loci virAG and bprC, which in turn induce the hcp and tssAB loci, encoding T6SS1 tube and sheath proteins [8,35]. Interestingly, our
RNAseq and qRT-PCR analyses revealed that BsaN also acts to repress transcription of T3SS3 apparatus genes in the bsaM and bsaN operons that are otherwise directly activated by the upstream regulator BprP. It is possible that BsaN mediates repression indirectly as the bsaM and bsaN intergenic region lacks a recognizable BsaN binding motif (see below). It is unlikely, however, that repression occurs due to decreased expression of bprP since its transcription is unchanged in a ΔbsaN Epigenetics inhibitor mutant. Taken together, these findings demonstrate that BsaN plays a dual role in the regulation of T3SS3; one in coordinating translocon and effector transcription,
and a second in preventing costly synthesis of T3SS3 apparatus components that are no longer required. Given the critical role of T3SS3 and T6SS1 in causing disease, BsaN/BicA could be considered a central regulator of B. pseudomallei mammalian virulence. Virulence Cyclin-dependent kinase 3 studies in mice support this notion, since the ΔbsaN mutant was unable to cause disease  in contrast to the ΔbspR mutant, which produced a more chronic infection in mice compared to wildtype bacteria . In addition to loci associated with T3SS3 and T6SS1, 41 other genes with potential roles in virulence were also found by RNAseq to be positively regulated by BsaN, most notably the bimBCAD intracellular motility operon and tssM. Regulation of bimA has been shown to be through virAG , explaining why no BsaN motif was identified for the operon. While bimA encodes an autotransporter protein that nucleates and polymerizes host cell actin to facilitate intracellular motility and cell-cell spread by the bacteria , the functions of the other loci in the bim operon are unknown.