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Biology · 术语表

什么是 Operon, repressor, operator？

Definition 20.3 University Biology — Year 1 · 第 20 章 — Control of Gene Expression

An operon is a group of bacterial genes transcribed together from one promoter into one messenger, and so controlled together. The lac operon of E. coli comprises three genes for the use of lactose — lacZ ( $\beta$ -galactosidase), lacY (the lactose permease that imports it) and lacA — behind a promoter and an operator, a short sequence overlapping the promoter. A separate gene, lacI, makes the lac repressor, a protein that binds the operator and blocks the polymerase. Lactose, converted in the cell to allolactose, is the inducer: it binds the repressor, changes its shape, and makes it let go of the operator. The operon is thus off unless lactose is present — negative control lifted by induction.

The lac operon. Without lactose the repressor sits on the operator and the polymerase cannot start; with lactose the inducer pulls the repressor off and the three genes are transcribed into one messenger.

示例

Example 20.7 (Two partial diploids)

$I^-\,O^+\,Z^+ / I^+\,O^+\,Z^-$ : the $I^+$ copy makes repressor that binds the $O^+$ next to $Z^+$ ; inducible — the mutation is complemented. $I^+\,O^c\,Z^+ / I^+\,O^+\,Z^-$ : the only working $Z$ sits behind an operator the repressor cannot bind; constitutive — the normal operator on the other copy cannot help, since it controls only the broken $Z$ .

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