And the negative control is the trp operon.

的例是色氨酸。

Well a negative control we learned about from the trp operon.

好的，我们从色氨酸中了解到的概念。

An operator sits right between the promoter and the genes.

位于启动和因之间。

So the tryptophan fits again and it's going to turn off.

因此，色氨酸再次充足，它将再次关闭（色氨酸的表达）。

In other words it lacks these little prongs we'll say that fit in the operator.

换句话说，它缺少那些能够嵌入的“小突起”。

In other words, now the repressor doesn't fit in the operator anymore.

换言之，现在阻遏蛋白无法再与结合。

And so this would be, when the repressor is here the operator is now in the off position.

因此，当阻遏蛋白在此处时，处于关闭状态。

Positive control example I'll give you is the lac operon.

我给你举的一个正的例是乳糖。

And the other thing they'll have in an operon is called an operator.

在中，另一个重要的组成部分叫做因。

A repressor will plug right into the operator, so it's going to fit right here, and as long as the repressor is available, RNA polymerase can't get on.

阻遏蛋白会正好嵌入中，因此它将恰好适应这里， 只要阻遏蛋白存在，RNA聚合酶就无法进入。

And so let's talk about how this works is the lac operon in bacteria because this the first one we really started to understand.

那么，让我们来谈谈这个机制是如何在细菌的乳糖中运作的，因为这是我们最先开始理解的一个例。