2 Catabolite Repression 1 Figure 9 The Diauxic

2. 降解�物的阻遏 Catabolite Repression ： 1）二次生��象及其机 制： 分解葡萄糖的酶—— �成�（固有�） 分解乳糖的酶——�� 酶， 受葡萄糖分解代��物的 �控。 Figure 9. The Diauxic Growth Curve of E. coli grown in limiting concentrations of a mixture of glucose and lactose

1）c. AMP与CAP结合。 2）当c. AMP与CAP复合 物结合在启动子上 , RNApolase 才与启动子 结合，转录进行。 3）当缺少c. AMP和CAP 时, RNApolase不能与启动 子结合。 Figure 10. Catabolite repression is positive control of the lac operon. The effect is an increase in the rate of transcription.

This assortment of genes and their regulatory regions is called the Lac operon. The Lac operon has been examined in detail. Here is a diagram of it:

Element Operator (Lac. O) Promoter (Lac. P) purpose binding site for repressor binding site for RNA polymerase gene encoding lac repressor protein Repressor (Lac. I) Binds to DNA at operator and blocks binding of RNA polymerase at promoter Pi promoter for Lac. I CAP binding site for c. AMP/CAP complex

When lactose is present

When the inducer (lactose) is removed

When levels of glucose in the cell are high