【正文】 araC的表達受到自身產(chǎn)物 AraC的自動調(diào)控。 ? 細胞中 AraC蛋白質(zhì)穩(wěn)態(tài)水平的測量表明，阻遏araC轉(zhuǎn)錄大約需要 40個 AraC。 ? 阿拉伯糖作為 ，可以誘導 ara操縱子的轉(zhuǎn)錄。 ? ? 然而當阿拉伯糖水平高，而葡萄糖水平低（ cAMP高）時， CAPcAMP復合物能夠與 ara操縱子中的 CAP結(jié)合部位結(jié)合，使 DNA突環(huán)打開。阿拉伯糖與AraC結(jié)合似乎改變了 AraC同源二聚體化特性和促進了 AraCCAP復合物的形成。 ? 當由于 araBAD編碼的蛋白質(zhì)的代謝使得阿拉伯糖水平下降時， AraC又轉(zhuǎn)換成一個阻遏物，同時araBAD轉(zhuǎn)錄減少，此時盡管 CAPcAMP復合物仍然存在于細胞中。 ? When the araC protein is bound to the operator araO1, transcription from PC is prevented. ? When arabinose levels are low, the AraC protein acts as a repressor and binds to two operator sites, araO1 and araO2, as well as to araI. ? Binding to araO1 inhibits transcription of the araC gene itself. Thus, araC is autoregulated at the level of its own transcription. AraC molecules bound to araO2 and araI interact with each other to form a DN