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Bradyrhizobium japonicum NnrR, a Denitrification Regulator, Expands the FixLJ-FixK2 Regulatory Cascade. Socorro Mesa, 2003.In Bradyrhizobium japonicum, a gene named nnrR was identified which encodes a protein with high similarity to FNR/CRP-type transcriptional regulators . Mutant strains carrying an nnrR null mutation were unable to grow anaerobically in the presence of nitrate or nitrite, and they lacked both nitrate and nitrite reductase activities . Anaerobic activation of an nnrR'-'lacZ fusion required FixLJ and FixK2 . In turn, N oxide-mediated induction of nir and nor genes encoding nitrite and nitric oxide reductase, respectively, depended on NnrR . Thus, NnrR expands the FixLJ-FixK2 regulatory cascade by an additional control level which integrates the N oxide signal required for maximal induction of the denitrification genes . Role of the Salmonella Pathogenicity Island 1 (SPI-1) Protein InvB in Type III Secretion of SopE and SopE2, Two Salmonella Effector Proteins Encoded Outside of SPI-1. Kristin Ehrbar, 2003.Salmonella enterica subspecies 1 serovar Typhimurium encodes a type III secretion system (TTSS) within Salmonella pathogenicity island 1 (SPI-1) . This TTSS injects effector proteins into host cells to trigger invasion and inflammatory responses . Effector proteins are recognized by the TTSS via signals encoded in their N termini . Specific chaperones can be involved in this process . The chaperones InvB, SicA, and SicP are encoded in SPI-1 and are required for transport of SPI-1-encoded effectors . Several key effector proteins, like SopE and SopE2, are located outside of SPI-1 but are secreted in an SPI-1-dependent manner . It has not been clear how these effector proteins are recognized by the SPI-1 TTSS . Using pull-down and coimmunoprecipitation assays, we found that SopE is copurified with InvB, the known chaperone for the SPI-1-encoded effector protein Sip/SspA . We also found that InvB is required for secretion and translocation of SopE and SopE2 and for stabilization of SopE2 in the bacterial cytosol . Our data demonstrate that effector proteins encoded within and outside of SPI-1 use the same chaperone for secretion via the SPI-1 TTSS .
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