Oehler Stefan, Alberti Siegfried, Müller-Hill Benno
IMBB-FoRTH, PO Box 1385, GR-71110 Heraklion, Crete, Greece.
Nucleic Acids Res. 2006 Jan 23;34(2):606-12. doi: 10.1093/nar/gkj453. Print 2006.
In vivo induction of the Escherichia coli lactose operon as a function of inducer concentration generates a sigmoidal curve, indicating a non-linear response. Suggested explanations for this dependence include a 2:1 inducer-repressor stoichiometry of induction, which is the currently accepted view. It is, however, known for decades that, in vitro, operator binding as a function of inducer concentration is not sigmoidal. This discrepancy between in vivo and in vitro data has so far not been resolved. We demonstrate that the in vivo non-linearity of induction is due to cooperative repression of the wild-type lac operon through DNA loop formation. In the absence of DNA loops, in vivo induction curves are hyperbolic. In the light of this result, we re-address the question of functional molecular inducer-repressor stoichiometry in induction of the lac operon.
大肠杆菌乳糖操纵子在体内的诱导作用随诱导剂浓度的变化产生一条S形曲线，表明存在非线性反应。对于这种依赖性的解释包括诱导时诱导剂与阻遏物的化学计量比为2:1，这是目前被广泛接受的观点。然而，几十年来人们都知道，在体外，操纵基因结合随诱导剂浓度的变化并非S形。体内和体外数据之间的这种差异至今尚未得到解决。我们证明，体内诱导的非线性是由于野生型乳糖操纵子通过DNA环形成的协同阻遏作用。在没有DNA环的情况下，体内诱导曲线呈双曲线。鉴于这一结果，我们重新探讨了乳糖操纵子诱导过程中功能性分子诱导剂 - 阻遏物化学计量比的问题。
