Hall B G
Genetics. 1978 Dec;90(4):673-81. doi: 10.1093/genetics/90.4.673.
In Escherichia coli, the wild-type repressor of ebg (evolved beta-galactosidase) enzyme synthesis, specified by the ebgR+ gene, responds very weakly to lactulose (fructose-beta-D-galactopyranoside). Selection for a functional repressor that responds strongly to lactulose as an inducer reveals the existence of ebgR+L mutants, which occur spontaneously at a frequency of about 2 X 10(-10) . EBGR+L mutants are pleiotropic in that they specify ebg repressor with a greatly increased response to lactulose, lactose, galactose-arabinoside and methyl-galactoside as inducers. Selection of ebgR+L mutants is discussed within the framework of directed evolution of a regulatory function.
在大肠杆菌中，由ebgR⁺基因指定的ebg（进化型β-半乳糖苷酶）酶合成的野生型阻遏物对乳果糖（果糖-β-D-吡喃半乳糖苷）的反应非常微弱。选择一种对乳果糖作为诱导物有强烈反应的功能性阻遏物，发现了ebgR⁺L突变体，其自发出现的频率约为2×10⁻¹⁰。EBGR⁺L突变体具有多效性，因为它们指定的ebg阻遏物对乳果糖、乳糖、半乳糖阿拉伯糖苷和甲基半乳糖苷作为诱导物的反应大大增强。在调节功能的定向进化框架内讨论了ebgR⁺L突变体的选择。
