In Escherichia coli, the wild-type repressor of ebg (evolved β-galactosidase) enzyme synthesis, specified by the ebgR+ gene, responds very weakly to lactulose (fructose-β-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.
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机译：在大肠杆菌中，由ebgR + 基因指定的ebg（进化的β-半乳糖苷酶）酶的野生型阻遏物对乳果糖（果糖-β-D-半乳糖吡喃糖苷）的响应非常弱。选择对乳果糖作为诱导剂有强烈反应的功能阻遏物表明存在ebgR + L 突变体，该突变体以约2 x 10 -10 的频率自发出现。 ebgR + L 突变体具有多效性，因为它们指定了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的诱导反应大大增加。在调节功能的定向进化框架内讨论了ebgR + L 突变体的选择。
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