大肠杆菌MetJ的基因修饰对其蛋氨酸产量的影响

采用1-甲基-3-硝基-1-亚硝基胍基因突变法,得到大肠杆菌K-12的耐蛋氨酸类似物突变体。经过发酵测试,突变菌株获得1 020 mg/L的L-蛋氨酸产量。研究结果表明:L-蛋氨酸生物合成过程中的2个关键酶,即胱硫醚γ-合酶与胱硫醚β-裂解酶,在L-蛋氨酸发酵过程中未受到蛋氨酸的反馈阻遏。采用PCR方法对突变体的MetJ蛋白克隆并进行基因测序可知,野生型的第54位的丝氨酸基因被替换为天冬氨酰,使得反馈阻遏作用消除,从而有效提高L-蛋氨酸的发酵产量。

Effect of Gene Modification in Escherichia coli MetJ on Its L-met Production

Gene mutation was carried out using N-methyl-N′-nitro-N-nitrosoguanidine. L-met-analogue-resistant mutants were derived from Escherichia coli K-12. The mutants produced 1 020 mg/L L-met in the fermentation test. It was confirmed that two key enzymes ,cystathionine γ-synthase and cystathionineβ-lyase were not repressed by excess of L-met during fermentation. MetJ protein was cloned and sequenced by the PCR. It was observed that serine at position 54 was replaced by asparaginate ,which enhanced L-met production because of the depression of L-met biosynthetic enzymes.