Molecular characterization and expression analysis of the anthranilate synthase gene of Pseudomonas syringae subsp. savastanoi

The trpE gene, which encodes the large component of the enzyme anthranilate synthase, was isolated from a Pseudomonas syringae subsp. savastanoi (P. savastanoi) cosmid library. Cosmids that complemented an Escherichia coli trpE mutation contained a gene whose product is 86% homologous at the deduced amino acid level to TrpE of Pseudomonas aeruginosa and Pseudomonas putida. Amino acid sequence comparison with other TrpE sequences revealed the existence of conserved regions between the procaryotic and eucaryotic polypeptide sequences analyzed, regions that might be of functional importance. We also report on studies on the expression pattern of this gene. We analyzed the promoter activity of a trpE::lacZ transcriptional fusion, the relative amount of trpE steady-state mRNA, and the activity of anthranilate synthase from cells grown in minimal medium with or without exogenously added tryptophan and in complete medium. We concluded that under the conditions tested, expression of the trpE gene of P. savastanoi is independent of the concentration of tryptophan in the culture medium. Implications of such an expression pattern on the virulence of this bacterium are discussed.