Multiple copies of a DNA sequence from Pseudomonas syringae pathovar phaseolicola abolish thermoregulation of phaseolotoxin production.
Phaseolotoxin, a phytotoxin of Pseudomonas syringae pv. phaseolicola, is produced at 18 degrees C but not at 28 degrees C. Here we report that a fragment (24.4 kb) cloned from the wild-type strain, which does not harbour a gene(s) involved in phaseolotoxin biosynthesis, abolishes this thermoregulation in the wild type and suppresses a Tox- mutant at both temperatures. A subclone harbouring a 485 bp fragment contains motifs that are characteristic of DNA-binding sites. In mobility shift assays we have detected a protein(s) from the wild-type and the mutant strains, grown at appropriate temperatures, that specifically binds to the fragment containing the DNA-binding motifs. We propose that the binding protein is a repressor which is 'titrated' by this fragment when it is present in the cell on a multiple copy plasmid, thus allowing expression of phaseolotoxin genes.
Rowley
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KB
Department of Plant Pathology, University of Hawaii, Honolulu 96822.
Clements
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Mandel
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Humphreys
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Patil
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D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D004269:DNA, Bacterial / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005098:Exotoxins / Q000096:biosynthesis*; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009952:Ornithine / Q000031:analogs & derivatives; D016133:Polymerase Chain Reaction; D011549:Pseudomonas / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D013696:Temperature
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D005098:Exotoxins; C021234:phaseolotoxin; D009952:Ornithine