Rainwater S, Silverman P M
Program in Molecular and Cell Biology, Oklahoma Medical Research Foundation, Oklahoma City 73104.
J Bacteriol. 1990 May;172(5):2456-61. doi: 10.1128/jb.172.5.2456-2461.1990.
An existing cpxA(Ts) mutant was resistant to amikacin at levels that inhibited completely the growth of a cpxA+ and a cpxA deletion strain and failed to grow as efficiently on exogenous proline. These properties are similar to those of mutants altered in a gene mapped to the cpxA locus and variously designated as ecfB, ssd, and eup. The amikacin resistance phenotype of the cpxA mutant was inseparable by recombination from the cpxA mutant phenotype (inability to grow at 41 degrees C without exogenous isoleucine and valine) and was recessive to the cpxA+ allele of a recombinant plasmid. Using methods that ensured independent mutations in the cpxA region of the chromosome, we isolated six new amikacin-resistant mutants following nitrosoguanidine mutagenesis. Three-factor crosses mapped the mutations to the cpxA locus. When transferred by P1 transduction to a cpxB11 Hfr strain, each of the mutations conferred the Tra- and Ilv- phenotypes characteristic of earlier cpxA mutants. Two of the new mutations led to a significantly impaired ability to utilize exogenous proline, and four led to partial resistance to colicin A. Two of the new cpxA alleles were recessive to the cpxA+ allele, and four were dominant, albeit to different degrees. On the basis of these data, we argue that cpxA, ecfB, eup, and ssd are all the same gene. We discuss the cellular function of the cpxA gene product in that light.
一个现有的cpxA（温度敏感型）突变体对丁胺卡那霉素具有抗性，其抗性水平能完全抑制cpxA+菌株和cpxA缺失菌株的生长，并且在外源脯氨酸上生长效率较低。这些特性与在定位于cpxA位点的一个基因中发生改变的突变体相似，该基因有不同的命名，如ecfB、ssd和eup。cpxA突变体的丁胺卡那霉素抗性表型通过重组与cpxA突变体表型（在没有外源异亮氨酸和缬氨酸的情况下不能在41℃生长）不可分离，并且对重组质粒的cpxA+等位基因是隐性的。使用确保染色体cpxA区域独立突变的方法，我们在亚硝基胍诱变后分离出六个新的丁胺卡那霉素抗性突变体。三因子杂交将这些突变定位到cpxA位点。当通过P1转导转移到cpxB11 Hfr菌株时，每个突变都赋予了早期cpxA突变体特有的Tra-和Ilv-表型。其中两个新突变导致利用外源脯氨酸的能力显著受损，四个导致对大肠菌素A的部分抗性。两个新的cpxA等位基因对cpxA+等位基因是隐性的，四个是显性的，尽管程度不同。基于这些数据，我们认为cpxA、ecfB、eup和ssd都是同一个基因。我们据此讨论了cpxA基因产物的细胞功能。
