Rowley K B, Clements D E, Mandel M, Humphreys T, Patil S S
Department of Plant Pathology, University of Hawaii, Honolulu 96822.
Mol Microbiol. 1993 May;8(3):625-35. doi: 10.1111/j.1365-2958.1993.tb01606.x.
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.
菜豆毒素是丁香假单胞菌菜豆致病变种的一种植物毒素，在18℃时产生，而在28℃时不产生。在此我们报道，从野生型菌株克隆的一个片段（24.4 kb），该野生型菌株不含有参与菜豆毒素生物合成的基因，它消除了野生型中的这种温度调节，并在两个温度下都抑制了一个Tox-突变体。一个含有485 bp片段的亚克隆包含DNA结合位点特有的基序。在凝胶迁移实验中，我们检测到了在适当温度下生长的野生型和突变型菌株中的一种蛋白质，它能特异性结合含有DNA结合基序的片段。我们提出，该结合蛋白是一种阻遏物，当它以多拷贝质粒形式存在于细胞中时，会被这个片段“滴定”，从而使菜豆毒素基因得以表达。
