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甘蓝黑腐病黄单胞菌（ＸａｎｔｈｏｍｏｎａｓｃａｍｐｅｓｔｒｉｓＰｖ．ｃａｍｐｅｓｔｒｉｓ）产生的胞外蛋白酶Ⅰ在致病的早期阶段起重要作用，该酶以及其它胞外酶和胞外多糖的合成受一致病因子调控基因簇（ｒＰｆ基因簇）的正向调控。本研究利用带有β－半乳糖苷酶报道基因（ｌａｃＺ）的转座子Ｔｎ５－Ｂ２０诱变蛋白酶Ⅰ基因克隆，获得了ｌａｃＺ在蛋白酶Ⅰ基因启动子控制下表达的Ｔｎ５－Ｂ２０插入突变质粒。通过将这种突变质粒导入野生型和各ｒｐｆ基因突变体菌株后，测定ｌａｃＺ基因在细胞生长周期中的表达水平，不仅进一步证实了这些ｒｐｆ基因对蛋白酶Ⅰ基因的正向调控作用，而且明确了它们的调控水平．发现ｒｐｆＡ、ｒｐｆＣ、ｒｐｆＥ、ｒｐｆＧ或ｒｐｆＨ突变后，蛋白酶Ⅰ基因的转录会降低９０％左右，而ｒｐｆＢ突变后，蛋白酶Ⅰ基因的转录只降低４８％。
Extracellular protease I produced by Xanthomonas campestrisPv.campestris plays an important role in the early stages of pathogenicity and the synthesis of this enzyme, as well as of other extracellular enzymes and exopolysaccharides, is regulated by a consensus pathogen-regulated gene cluster (RPf gene cluster) positive regulation. In this study, Tn5-B20 mutant was cloned by using the transposon Tn5-B20 with β-galactosidase reporter gene (lacZ) to mutate the protease Ⅰ gene. The mutant Tn5-B20 was expressed under the control of protease Ⅰ promoter. By introducing this mutant plasmid into wild-type and mutant strain of rpf gene and measuring the expression level of lacZ gene in cell cycle, not only the positive regulatory effect of these rpf gene on protease Ⅰ gene was further confirmed Their level of regulation. When rpfA, rpfC, rpfE, rpfG or rpfH mutations were found, the transcription of the protease I gene was reduced by about 90%, whereas the transcription of the protease I gene was reduced by only 48% after rpfB mutation.