Qu J N, Makino S I, Adachi H, Koyama Y, Akiyama Y, Ito K, Tomoyasu T, Ogura T, Matsuzawa H
Department of Biotechnology, University of Tokyo, Japan.
J Bacteriol. 1996 Jun;178(12):3457-61. doi: 10.1128/jb.178.12.3457-3461.1996.
Escherichia coli tolZ mutants are tolerant to colicins E2, E3, D, Ia, and Ib (Tol-), can grow on glucose but not on succinate or other nonfermentable carbon sources (Nfc-), and show temperature-sensitive growth (Ts). A 1.8-kb DNA fragment that complemented the tolZ mutation was cloned. The DNA fragment was sequenced, and one open reading frame was found. This frame was identical to a part of the E. coli FtsH protein, an ATP-dependent metalloprotease that binds to the cytoplasmic membrane. The tolZ gene was located at 69 min on the E. coli genetic map, and the mutation was complemented by a plasmid carrying the ftsH gene, indicating that the tolZ gene is identical to the ftsH gene. The mutated tolZ21 gene was also cloned and sequenced and was found to have a single base change that caused an amino acid alteration of His-418 to Tyr in the FtsH protein. The tolZ21 mutant showed Hfl- (high frequency of lysogenization) and Std- (stop transfer-defective) pheno-types, both of which are due to a mutation in the ftsH (hflB) gene. However, the ftsH1, ftsH101, and hflB29 mutants did not show Tol- and Nfc phenotypes. The tolZ21 mutant was found to have a suppressor mutation, named sfhC, which allowed cells to survive. The sfhC mutation alone caused no Tol-, Nfc-, Ts, or Hfl- phenotypes in the tolZ21 mutant.
大肠杆菌tolZ突变体对大肠杆菌素E2、E3、D、Ia和Ib具有耐受性（Tol-），能在葡萄糖上生长，但不能在琥珀酸盐或其他非发酵碳源上生长（Nfc-），并且表现出温度敏感生长（Ts）。克隆了一个能互补tolZ突变的1.8kb DNA片段。对该DNA片段进行了测序，发现了一个开放阅读框。这个框架与大肠杆菌FtsH蛋白的一部分相同，FtsH蛋白是一种与细胞质膜结合的ATP依赖性金属蛋白酶。tolZ基因位于大肠杆菌遗传图谱的69分钟处，该突变被携带ftsH基因的质粒互补，这表明tolZ基因与ftsH基因相同。突变的tolZ21基因也被克隆和测序，发现有一个单碱基变化，导致FtsH蛋白中His-418突变为Tyr。tolZ21突变体表现出Hfl-（高频溶原化）和Std-（停止转移缺陷）表型，这两种表型都是由ftsH（hflB）基因突变引起的。然而，ftsH1、ftsH101和hflB29突变体没有表现出Tol-和Nfc表型。发现tolZ21突变体有一个抑制突变，命名为sfhC，它使细胞能够存活。单独的sfhC突变在tolZ21突变体中不会引起Tol-、Nfc-、Ts或Hfl-表型。
