Identification of the transcriptional regulatory gene of histidase and urocanase in Pseudomonas aeruginosa -Regulation of histidase and urocanase expression-

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Pseudomonas aeruginosa is a typical opportunistic bacterial pathogen that can grow under poor nutrient conditions. Histidine utilization as a sole source of carbon and nitrogen is a distinctive feature of P.aeruginosa, which decompose and utilize a variety of nutrients and complex compounds using various catabolite pathways. When wild-type P.aeruginosa PAO1 cells were cultured in minimal medium P (MMP) containing 20mM histidine, synthesis of histidase and urocanase was detected in crude extract at 3186±118 (U/mg-proteins) and 243±3 (10-3 U/mg-proteins), respectively. It was determined that the synthesis of these enzymes was induced by histidine because limited enzyme synthesis was observed in MMP containing 20mM of glutamate. In contrast, PAO4399, the spontaneous mutant of PAO1, can synthesize histidase and urocanase sufficiently under the nutrient conditions of MMP containing histidine or glutamate. A nucleotide sequence analysis of PAO4399 showed a C to G transition at nt 441 of the PA5105 gene, with this mutation causing an amino acid change of the tyrosine codon (TAC) Tyr 147 to stop codon (TAG). In the case of PAO4816, the knockout mutant strain of PAO1 with an inserted gentamicin (Gm)-cassette in the PA5105 gene, the cells grown in MMP containing 20mM of histidine or glutamate synthesized histidase and urocanase constitutively, in the same manner as PAO4399. The PA5105 gene product is highly homologous with the hutC gene product of Pseudomonas putida, which regulates histidase and urocanase gene expression. These findings support the role of the PA5105 gene of P.aeruginosa PAO1 as a repressor-type hutC gene that regulates histidase and urocanase synthesis under histidine-dependent nutrient conditions.

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