Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA.
Cell Rep. 2012 Jul 26;2(1):150-61. doi: 10.1016/j.celrep.2012.06.004. Epub 2012 Jul 12.
A canonical quantitative view of transcriptional regulation holds that the only role of operator sequence is to set the probability of transcription factor binding, with operator occupancy determining the level of gene expression. In this work, we test this idea by characterizing repression in vivo and the binding of RNA polymerase in vitro in experiments where operators of various sequences were placed either upstream or downstream from the promoter in Escherichia coli. Surprisingly, we find that operators with a weaker binding affinity can yield higher repression levels than stronger operators. Repressor bound to upstream operators modulates promoter escape, and the magnitude of this modulation is not correlated with the repressor-operator binding affinity. This suggests that operator sequences may modulate transcription by altering the nature of the interaction of the bound transcription factor with the transcriptional machinery, implying a new layer of sequence dependence that must be confronted in the quantitative understanding of gene expression.
经典的转录调控定量观点认为，操纵序列的唯一作用是设定转录因子结合的概率，而操纵子占据决定基因表达水平。在这项工作中，我们通过在大肠杆菌中，将不同序列的操纵子置于启动子的上游或下游，来描述体内的抑制和体外 RNA 聚合酶的结合，以此来检验这个观点。令人惊讶的是，我们发现结合亲和力较弱的操纵子可以产生比结合亲和力较强的操纵子更高的抑制水平。结合在上游操纵子上的阻遏物调节启动子逃避，这种调节的幅度与阻遏物-操纵子结合亲和力无关。这表明，操纵序列可能通过改变结合的转录因子与转录机制的相互作用的性质来调节转录，这意味着在定量理解基因表达时，必须面对一个新的序列依赖层。
