Study on Iron Regulon in Pseudomonas aeruginosa

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The Pseudomonas aeruginosa genes for production of several pathogenic factors (represented by pyoverdin, pyochelin, alkaline proteinase, and exotoxin A) belong to the iron regulon. The transcription of these genes under iron-rich conditions is repressed by an activated from of Fur, a global repressor of the regulon. This regulator often controls the transcription of some genes by repressing the transcription of pvdS, a gene encoding an alternative sigma factor of RNA polymease that is at least required for transcription of the structural genes for pyoverdin and alkaline proteinase. In this study, the fur gene was analyzed and two methods were devised to identify novel genes in the iron regulon. A 14-kb chromosomal region covering the fur gene was cloned. Its sequence analysis demonstrated that the Fur box, a consensus sequence for binding of Fur, was not found at the upstream region of the fur gene, suggesting that the fur transcription is not auto-regulated by Fur. Genetic attempts we … More re unsuccessful to isolate the chromosomal null mutations of the fur gene as well as the grpE and dnaJ genes that are located downstream of fur, unless the wild-type alleles of these three genes were supplied in trans. These results indicated that the latter two genes are essential and that Fur regulates positively the expression of the unidentified gene(s) whose functions are essential under normal growth conditions. A number of mutants were isolated in each of which a promoter-probe transposon carrying a promoterless gfp gene was inserted into the chromosome. Among such mutants, three mutants expressed the gfp gene preferentially only under iron-rich conditions and three other mutants preferentially only under iron-limiting conditions. The chromosomal regions flanking these six mutation sites were isolated. It has been well known that the iron regulon includes the genes whose protein products are localized to the membrane fraction, and we established a biochemical method by which such products are easily detected by the two-dimension gel electrophoresis. Less