乳 乳糖操纵子 CAP∽cAMP复合物形成 糖 RNA Polymerase +自→ 正调控 CAP cAMP CAP-AMPcompi 操 o Lacz LacY LacA 纵 负调挖 阻遇蛋白ms0mgs δ因子 mRNA CAR-CAMP R 乳糖分子 complex 负 The binding of the CAP-cAMP complex to the promoter site is requiredfor transcription of the lac operon. The presence of this complex is closely associated with the presence 正 of glucose in the celL. As the concentration of glucose increases the amount of cAMP decreases. As the caMP decreases, the amount of complex decreases. This decrease in the 调 complex inactivates the promoter and the lac operon is turned off. Because the CAP-cAMP 控 complex is needed for transcription, the complex exerts a positive control over the expression of the lac operon.细胞中葡萄糖浓度高,ATP更多,AP减少, CAP-cAMP也减少,关闭转录乳糖操纵子负正调控