Molecular mechanism for establishment of signal-dependent regulation in the PhoP/PhoQ system.
In this report, we demonstrate that H-NS is essential for establishing the Mg(2+)-responsive transcriptional regulation of the PhoP regulon in Salmonella. Deletion of this regulatory gene abolished the transcriptional repression of PhoP-activated genes when bacteria were grown in high environmental Mg(2+), thus stimulating expression of phoP and other PhoP regulon genes. In the absence of H-NS, transcriptional activation was PhoP-dependent for those genes only activated by PhoP, but was PhoP-independent for those genes activated by both PhoP and SlyA. The H-NS protein footprints the phoP promoter in a sequence located upstream of the PhoP box; mutation of this cis-acting factor abolished transcriptional repression of the phoP gene equivalent to the phenotype exhibited in the hns mutant. Further results showed that H-NS gel shifts other PhoP regulon promoters, indicating that a PhoP-activated gene would be transcriptionally repressed via direct H-NS binding and inhibition of its activator PhoP. Furthermore, H-NS footprints a newly identified SlyA box and the reverse PhoP box in the pagC promoter, suggesting that both SlyA and PhoP compete with this regulatory protein. Therefore, H-NS should pair with SlyA and PhoP to establish a forward regulatory loop to regulate expression of pagC, and perhaps other PhoP- and SlyA-dependent genes.
Kong
Wei
W
Center for Infectious Diseases and Vaccinology at the Biodesign Institute and The School of Life Sciences, Arizona State University, Tempe, Arizona 85287-4501, USA.
Weatherspoon
Natasha
N
Shi
Yixin
Y
D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D003850:Deoxyribonuclease I / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008274:Magnesium / Q000737:chemistry; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D019779:Salmonella enterica / Q000378:metabolism; D015398:Signal Transduction; D014158:Transcription, Genetic; D015533:Transcriptional Activation
D001426:Bacterial Proteins; C079792:PhoQ protein, Bacteria; C061064:PhoP protein, Bacteria; D003850:Deoxyribonuclease I; D008274:Magnesium