Misra R, Reeves P R
Department of Microbiology, University of Sydney, New South Wales, Australia.
J Bacteriol. 1987 Oct;169(10):4722-30. doi: 10.1128/jb.169.10.4722-4730.1987.
Mutation in the tolC locus greatly reduces normal synthesis of OmpF, a major porin protein of Escherichia coli K-12. Experiments that use ompF-ompC chimeric genes demonstrate that a tolC mutation exerts its effect at either the promoter or the amino-terminal end of the ompF gene. Direct analysis of ompF mRNA from tolC+ and tolC strains showed that the amount of ompF transcript in the latter was greatly reduced. We have also observed that, in addition to reducing the amount of OmpF, a tolC mutation increases the level of OmpC protein to a much greater extent than occurs in an OmpF mutant and also increases micF RNA synthesis as shown by increased beta-galactosidase synthesis in a micF-lacZ fusion strain. Based on these observations, we suggest that an increased expression of the micF gene in a tolC mutant results in the reduced expression of ompF and that a major effect of the tolC mutation may be to push the porin-regulating system to favor ompC and micF to a greater extent than under high-osmolarity conditions.
tolC位点的突变极大地降低了大肠杆菌K - 12主要孔蛋白OmpF的正常合成。使用ompF - ompC嵌合基因的实验表明，tolC突变在ompF基因的启动子或氨基末端发挥作用。对tolC⁺和tolC菌株的ompF mRNA进行直接分析表明，后者中ompF转录本的量大大减少。我们还观察到，除了减少OmpF的量外，tolC突变使OmpC蛋白水平的增加程度远大于OmpF突变体，并且如micF - lacZ融合菌株中β - 半乳糖苷酶合成增加所示，tolC突变还增加了micF RNA的合成。基于这些观察结果，我们认为tolC突变体中micF基因表达的增加导致了ompF表达的降低，并且tolC突变的主要作用可能是使孔蛋白调节系统比在高渗透压条件下更倾向于ompC和micF。
