Prasad I, Schaefler S
J Bacteriol. 1974 Nov;120(2):638-50. doi: 10.1128/jb.120.2.638-650.1974.
In Escherichia coli wild-type cells, a mutation at the beta-glucoside regulatory gene (bglR(+) to bglR(-)) leads to simultaneous expression of inducible phospho-beta-glucosidase B (bglB(+)) and a beta-glucoside-specific species of enzyme II (beta-glucoside transport I [bglC(+)]); an additional mutation (bglS(+) to bglS4) allows these enzymes to be formed constitutively. The bgl alleles have been mapped in the following order: pyrE, bglA, bglB, bglS, bglR, bglC, ilvD. The back mutation in the regulatory allele (bglR(-) to bglR(+)) caused the cessation of the expression of the bglB(+), bglS(+) or bglS4, bglC(+) alleles. However, a mutation in a strain with bglB(+), bglS4, bglR8, bglC(+) alleles, at the ini site that lies between the bglS4 and the bglR8 allele, allowed the expression of the bglS4 and bglB(+) alleles, but showed no affect on the expression of the bglC(+) allele. It is suggested that the ini mutation possesses a promotor-type function that in the absence of regulatory allele function (bglR8) renews the functioning of only the bglS4 and bglB(+) alleles. The complementation studies have shown that the bglB(+), bglS(+) or bglS4, bglC(+) alleles are expressed only in cis to the bglR(-) allele. In the constitutive strain (bglB(+), bglS4, bglR(-), bglC(+)), the expressed bglS4 allele formed a soluble product that acts in trans over the bglB(+) and bglC(+) alleles and that appears effective only when the bglB(+) and the bglC(+) alleles are expressed in cis to the bglR(-) allele. It thus showed that the constitutive biosynthesis of phospho-beta-glucosidase B and beta-glucoside transport I is under positive control. Since the regulatory allele bglR(-) lies between the bglS4 and the blgC(+) alleles, and acts in cis, it appears that the mutation (bglR(+) to bglR(-)) allows the initiation of transcription in one direction to express the bglS4, bglB(+) alleles and in the other to express the bglC(+) allele. The structural genes bglB and bglC lie adjacent to the regulatory genes bglR and bglS, and the structural genes are coordinately controlled by the regulatory genes. It is, therefore, proposed that the bglB, bglS, bglR, bglC genes form a bgl operon.
在大肠杆菌野生型细胞中，β-葡萄糖苷调节基因发生突变（从bglR(+)突变为bglR(-)）会导致诱导型磷酸-β-葡萄糖苷酶B（bglB(+)）和一种β-葡萄糖苷特异性的酶II（β-葡萄糖苷转运I [bglC(+)]）同时表达；另一个突变（从bglS(+)突变为bglS4）可使这些酶组成型形成。bgl等位基因已按以下顺序定位：pyrE、bglA、bglB、bglS、bglR、bglC、ilvD。调节等位基因的回复突变（从bglR(-)突变为bglR(+)）导致bglB(+)、bglS(+)或bglS4、bglC(+)等位基因的表达停止。然而，在一个具有bglB(+)、bglS4、bglR8、bglC(+)等位基因的菌株中，位于bglS4和bglR8等位基因之间的ini位点发生突变，使得bglS4和bglB(+)等位基因得以表达，但对bglC(+)等位基因的表达没有影响。这表明ini突变具有启动子型功能，在没有调节等位基因功能（bglR8）的情况下，仅恢复bglS4和bglB(+)等位基因的功能。互补研究表明，bglB(+)、bglS(+)或bglS4、bglC(+)等位基因仅在与bglR(-)等位基因顺式排列时才表达。在组成型菌株（bglB(+)、bglS4、bglR(-)、bglC(+)）中，表达的bglS4等位基因形成一种可溶性产物，它可反式作用于bglB(+)和bglC(+)等位基因，并且仅当bglB(+)和bglC(+)等位基因与bglR(-)等位基因顺式排列时才显得有效。因此表明，磷酸-β-葡萄糖苷酶B和β-葡萄糖苷转运I的组成型生物合成受正调控。由于调节等位基因bglR(-)位于bglS4和blgC(+)等位基因之间，并顺式作用，看来突变（从bglR(+)到bglR(-)）允许转录在一个方向上起始以表达bglS4、bglB(+)等位基因，而在另一个方向上表达bglC(+)等位基因。结构基因bglB和bglC与调节基因bglR和bglS相邻，并且结构基因由调节基因协调控制。因此，有人提出bglB、bglS、bglR、bglC基因形成一个bgl操纵子。
