Dolph P J, Majerczak D R, Coplin D L
Department of Plant Pathology, Ohio State University, Wooster 44691.
J Bacteriol. 1988 Feb;170(2):865-71. doi: 10.1128/jb.170.2.865-871.1988.
We have previously cloned the genes for synthesis of capsular polysaccharide (cps) and slime from Erwinia stewartii in cosmid pES2144. In this study, pES2144 was shown to complement 14 spontaneous cps mutants. These mutants were characterized by probing Southern blots of mutant genomic DNA with pES2144; insertions were detected in four mutants and deletions in six mutants. Genetic and physical maps of the pES2144 cps region were constructed by subcloning, restriction analysis, and transposon mutagenesis with Tn5, Tn5lac, and Tn3HoHo1. Mutations affecting the ability of pES2144 to restore mucoidy to cps deletion mutants were located in five regions, designated cpsA to cpsE. None of the cps mutants were able to cause systemic wilting of corn plants, and mutations in cps regions B to E further abolished the ability of the bacterium to cause watersoaked lesions on seedlings. The gene for uridine-5'-diphosphogalactose 4-epimerase (galE) was linked to the cps genes on pES2144. In E. stewartii, galE was constitutively expressed, whereas the genes for galactokinase (galK) and galactose-1-phosphate uridyltransferase (galT) were inducible and not linked to galE. Thus, galE does not appear to be part of the gal operon in this species.
我们之前已在黏粒pES2144中克隆了来自斯氏欧文氏菌的荚膜多糖（cps）和黏液合成基因。在本研究中，pES2144被证明可互补14个自发的cps突变体。通过用pES2144探测突变体基因组DNA的Southern印迹来对这些突变体进行表征；在四个突变体中检测到插入，在六个突变体中检测到缺失。通过亚克隆、限制性分析以及用Tn5、Tn5lac和Tn3HoHo1进行转座子诱变构建了pES2144 cps区域的遗传图谱和物理图谱。影响pES2144恢复cps缺失突变体黏液性能力的突变位于五个区域，命名为cpsA至cpsE。没有一个cps突变体能够引起玉米植株的系统性萎蔫，并且cps区域B至E中的突变进一步消除了该细菌在幼苗上引起水渍状病斑的能力。尿苷-5'-二磷酸半乳糖4-表异构酶（galE）基因与pES2144上的cps基因相连。在斯氏欧文氏菌中，galE组成型表达，而半乳糖激酶（galK）和半乳糖-1-磷酸尿苷酰转移酶（galT）基因是可诱导的，并且不与galE相连。因此，galE在该物种中似乎不是半乳糖操纵子的一部分。
