Kim J F, Wei Z M, Beer S V
Department of Plant Pathology, Cornell University, Ithaca, New York 14853, USA.
J Bacteriol. 1997 Mar;179(5):1690-7. doi: 10.1128/jb.179.5.1690-1697.1997.
A 6.2-kb region of DNA corresponding to complementation groups II and III of the Erwinia amylovora hrp gene cluster was analyzed. Transposon mutagenesis indicated that the two complementation groups are required for secretion of harpin, an elicitor of the hypersensitive reaction. The sequence of the region revealed 10 open reading frames in two putative transcription units: hrpA, hrpB, hrcJ, hrpD, and hrpE in the hrpA operon (group III) and hrpF, hrpG, hrcC, hrpT, and hrpV in the hrpC operon (group II). From promoter regions of the hrpA, hrpC, and hrpN operons, sequences similar to those of the HrpL-dependent promoters of Pseudomonas syringae pathovars were identified with a consensus sequence of 5'-GGAAC-N17-18-CACTNAA-3'. The protein products of seven genes, hrpA, hrcJ, hrpE, hrpF, hrpG, hrcC, and hrpV, were visualized with a T7 polymerase/promoter expression system. HrcC, HrcJ, and HrpT sequences contained potential signal peptides, and HrcC appeared to be envelope associated based on a TnphoA translational fusion. Comparison of deduced amino acid sequences indicated that many of the proteins are homologous to proteins that function in the type III protein secretion pathway. HrcC is a member of the YscC-containing subgroup in the PulD/pIV superfamily of outer membrane proteins. HrcJ is a member of a lipoprotein family that includes YscJ of Yersinia spp., MxiJ of Shigella flexneri, and NolT of Rhizobim fredii. Additional similarities were detected between HrpB and YscI and between HrpE and YscL. HrcJ and HrpE were similar to flagellar biogenesis proteins FliF and FliH, respectively. In addition, HrpA, HrpB, HrcJ, HrpD, HrpE, HrpF, and HrcC showed various degrees of similarity to corresponding proteins of P. syringae. Comparison of hrp clusters with respect to gene organization and similarity of individual proteins confirms that the hrp systems of E. amylovora and P. syringae are closely related to each other and distinct from those of Ralstonia (Pseudomonas) solanacearum and Xanthomonas campestris. Possible implications of extensive similarities between the E. amylovora and P. syringae hrp systems in pathogenesis mechanisms are discussed.
对与解淀粉欧文氏菌hrp基因簇的互补群II和III相对应的一段6.2 kb的DNA区域进行了分析。转座子诱变表明，这两个互补群是过敏反应激发子harpin分泌所必需的。该区域的序列在两个推定的转录单元中揭示了10个开放阅读框：hrpA操纵子（III组）中的hrpA、hrpB、hrcJ、hrpD和hrpE，以及hrpC操纵子（II组）中的hrpF、hrpG、hrcC、hrpT和hrpV。从hrpA、hrpC和hrpN操纵子的启动子区域，鉴定出与丁香假单胞菌致病变种的HrpL依赖性启动子序列相似的序列，共有序列为5'-GGAAC-N17-18-CACTNAA-3'。用T7聚合酶/启动子表达系统观察到7个基因hrpA、hrcJ、hrpE、hrpF、hrpG、hrcC和hrpV的蛋白质产物。HrcC、HrcJ和HrpT序列含有潜在的信号肽，基于TnphoA翻译融合，HrcC似乎与包膜相关。推导的氨基酸序列比较表明，许多蛋白质与III型蛋白质分泌途径中起作用的蛋白质同源。HrcC是外膜蛋白PulD/pIV超家族中含YscC亚组的成员。HrcJ是脂蛋白家族的成员，该家族包括耶尔森氏菌属的YscJ、福氏志贺氏菌的MxiJ和费氏中华根瘤菌的NolT。在HrpB和YscI之间以及HrpE和YscL之间检测到其他相似性。HrcJ和HrpE分别与鞭毛生物合成蛋白FliF和FliH相似。此外，HrpA、HrpB、HrcJ、HrpD、HrpE、HrpF和HrcC与丁香假单胞菌的相应蛋白质表现出不同程度的相似性。就基因组织和单个蛋白质的相似性对hrp簇进行比较，证实了解淀粉欧文氏菌和丁香假单胞菌的hrp系统彼此密切相关，且与青枯雷尔氏菌（假单胞菌属）和野油菜黄单胞菌的hrp系统不同。讨论了解淀粉欧文氏菌和丁香假单胞菌hrp系统之间广泛相似性在致病机制中的可能意义。
