McClain M S, Blomfield I C, Eberhardt K J, Eisenstein B I
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor 48109-0620.
J Bacteriol. 1993 Jul;175(14):4335-44. doi: 10.1128/jb.175.14.4335-4344.1993.
The roles of fimB and fimE in the phase-variable expression of type 1 fimbriae in Escherichia coli were examined. A method was developed to study the effects of fimB and fimE on both recombination of the fim invertible element and fimbrial expression. The method used an allelic exchange procedure consisting of two steps. The first step, construction of intermediate strains, deleted fimB and fimE. This step locked the invertible element in either the on or the off orientation. The second step of the exchange procedure introduced either wild-type or mutant alleles of fimB and/or fimE into the chromosome of the intermediate strains. Analysis of the resulting strains supported the current, plasmid-based model of recombination. Unexpectedly, strains in which the invertible element was locked in the on orientation (either by mutation of both fimB and fimE or, in a control strain, by mutation of the left inverted repeat sequence of the invertible element) continued to exhibit phase-variable expression of type 1 fimbriae. A strain in which fimA was transcribed from the tac promoter continued to exhibit phase-variable fimbrial expression, suggesting that inversion-independent phase variation cannot be explained by variable transcription initiation of fimA.
研究了fimB和fimE在大肠杆菌1型菌毛相变表达中的作用。开发了一种方法来研究fimB和fimE对fim可逆元件重组和菌毛表达的影响。该方法采用了由两步组成的等位基因交换程序。第一步，构建中间菌株，缺失fimB和fimE。这一步将可逆元件锁定在开启或关闭方向。交换程序的第二步将fimB和/或fimE的野生型或突变等位基因引入中间菌株的染色体。对所得菌株的分析支持了当前基于质粒的重组模型。出乎意料的是，可逆元件被锁定在开启方向的菌株（要么通过fimB和fimE两者的突变，要么在对照菌株中通过可逆元件左反向重复序列的突变）继续表现出1型菌毛的相变表达。一个其中fimA从tac启动子转录的菌株继续表现出可变的菌毛表达，这表明与倒位无关的相变不能用fimA可变的转录起始来解释。
