Miki K, Lin E C
J Bacteriol. 1980 Sep;143(3):1436-43. doi: 10.1128/jb.143.3.1436-1443.1980.
Strains of Escherichia coli K-12 deleted in the native lac operon and bearing both a wild-type glpT operon encoding for sn-glycerol 3-phosphate (G3P) transport and a hybrid operon in which glpT operator and promoter regions are fused to the lacZ gene were constructed. In strains with such a hybrid operon, beta-galactosidase and beta-galactoside permease become inducible by G3P. In these mutants the function and maturation of the glpT-coded proteins should be distinguishable from the level of gene expression, since the beta-galactosidase activity can serve as an index of the latter. With the aid of such mutants, it was shown that: (i) the expressions of the two neighboring operons, glpT and glpA (encoding anaerobic G3P dehydrogenase), are not coordinate; (ii) upon induction, the appearance of the cytoplasmic beta-galactosidase activity preceded that of methyl-beta-D-thiogalactoside transport activity (requiring only a cytoplasmic membrane protein) by about 4 min and that of G3P transport activity (requiring both a cytoplasmic membrane protein and a periplasmic protein) by about 9 min; and (iii) when cells grown at several temperatures from 24 to 42 degrees C were measured for G3P transport activity at 30 degrees C, the activity increased with the growth temperature, indicating that, within the range studied, the rate of transport increases with the fluidity of membrane phospholipids.
构建了在天然乳糖操纵子中缺失的大肠杆菌K-12菌株，这些菌株带有一个编码sn-甘油3-磷酸（G3P）转运的野生型glpT操纵子和一个杂合操纵子，其中glpT操纵基因和启动子区域与lacZ基因融合。在具有这种杂合操纵子的菌株中，β-半乳糖苷酶和β-半乳糖苷通透酶可被G3P诱导。在这些突变体中，glpT编码蛋白的功能和成熟应与基因表达水平区分开来，因为β-半乳糖苷酶活性可作为后者的指标。借助这些突变体，结果表明：（i）两个相邻操纵子glpT和glpA（编码厌氧G3P脱氢酶）的表达不协调；（ii）诱导后，细胞质β-半乳糖苷酶活性的出现比甲基-β-D-硫代半乳糖苷转运活性（仅需要一种细胞质膜蛋白）提前约4分钟，比G3P转运活性（需要一种细胞质膜蛋白和一种周质蛋白）提前约9分钟；（iii）当在24至42摄氏度的几个温度下生长的细胞在30摄氏度下测量G3P转运活性时，活性随生长温度升高，表明在所研究的范围内，转运速率随膜磷脂流动性增加。
