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A New Heat Shock Gene, agsA, Which Encodes a Small Chaperone Involved in Suppressing Protein Aggregation in Salmonella enterica Serovar Typhimurium

Department of Microbiology and Molecular Genetics, Graduate School of Pharmaceutical Sciences, Chiba University, Inage-ku, Chiba 263-8522,¹ Kazusa DNA Research Institute, Kisarazu, Chiba 292-0812,² Department of Biological Science, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan³

Received 27 May 2003/ Accepted 14 August 2003

We discovered a novel small heat shock protein (sHsp) named AgsA (aggregation-suppressing protein) in the thermally aggregated fraction from a Salmonella enterica serovar Typhimurium dnaK-null strain. The -10 and -35 regions upstream of the transcriptional start site of the agsA gene are characteristic of ³²- and ⁷²-dependent promoters. AgsA was strongly induced by high temperatures. The similarity between AgsA and the other two sHsps of Salmonella serovar Typhimurium, IbpA and IbpB, is rather low (around 30% amino acid sequence identity). Phylogenetic analysis suggested that AgsA arose from an ancient gene duplication or amplification at an early evolutionary stage of gram-negative bacteria. Here we show that overproduction of AgsA partially complements the dnaK52 thermosensitive phenotype and reduces the amount of heat-aggregated proteins in both dnaK52 and rpoH mutants of Escherichia coli. These data suggest that AgsA is an effective chaperone capable of preventing aggregation of nonnative proteins and maintaining them in a state competent for refolding in Salmonella serovar Typhimurium at high temperatures.

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