Cronan J E
Department of Microbiology, University of Illinois, Urbana 61801.
J Biol Chem. 1988 Jul 25;263(21):10332-6.
In Escherichia coli biotin biosynthesis is repressed by high concentrations of exogenous biotin. This paper reports that upon high level production of the apo form of a biotinated protein, biotin operon expression was derepressed by 8-10-fold. The biotinated protein studied was the 1.3 S subunit of Propionibacterium shermanii, and transcarboxylase derepression was assayed by beta-galactosidase production in strains which carry a lacZ gene altered such that it is transcribed from biotin operon promoters. Depression of beta-galactosidase synthesis upon production of the apo 1.3 S protein was observed over a several hundred-fold range of biotin concentrations and also resulted in an increased level of biotin operon expression at maximally repressing biotin concentrations. Biotin operon derepression by apobiotin protein production seems a direct consequence of the properties of the biotin repressor protein which also functions as the ligase catalyzing the covalent attachment of biotin to apoproteins.
在大肠杆菌中，高浓度的外源生物素会抑制生物素的生物合成。本文报道，当生物素化蛋白的脱辅基形式大量产生时，生物素操纵子的表达会解除抑制，提高8至10倍。所研究的生物素化蛋白是谢氏丙酸杆菌的1.3S亚基，通过在携带经改造的lacZ基因的菌株中产生β-半乳糖苷酶来检测转羧酶的去抑制情况，改造后的lacZ基因可从生物素操纵子启动子转录。在数百倍的生物素浓度范围内，观察到脱辅基1.3S蛋白产生时β-半乳糖苷酶合成受到抑制，并且在最大程度抑制生物素浓度时，生物素操纵子的表达水平也有所提高。脱辅基生物素蛋白的产生导致生物素操纵子去抑制，这似乎是生物素阻遏蛋白特性的直接结果，该蛋白还作为连接酶催化生物素与脱辅基蛋白的共价连接。
