Zhou Y, Merkel T J, Ebright R H
Department of Chemistry, Rutgers University, New Brunswick, NJ 08855.
J Mol Biol. 1994 Nov 4;243(4):603-10. doi: 10.1016/0022-2836(94)90035-3.
CAP-dependent promoters can be divided into classes based on the position of the DNA site for CAP. In class I CAP-dependent promoters, the DNA site for CAP is located upstream of the DNA site for polymerase; the DNA site for CAP can be located at various distances from the transcription start point, provided that the DNS site for CAP and the DNA site for RNA polymerase are on the same face of the DNA helix. In class II CAP-dependent promoters, the DNA site for CAP overlaps the DNA site for RNA polymerase, replacing the -35 determinants for binding of RNA polymerase. In previous work, we have shown that a surface loop consisting of amino acid residues 152 to 166 of CAP is essential for transcription activation at the best-characterized class I CAP-dependent promoter, the lac promoter, and we proposed that this surface loop makes direct protein-protein contact with RNA polymerase in the ternary complex of lac promoter, CAP, and RNA polymerase. Here, we show that the surface loop consisting of amino acid residues 152 to 166 is essential for transcription activation at other class I CAP-dependent promoters and at a class II CAP-dependent promoter. We show further that the effects of alanine substitutions of residues 152 to 166 are qualitatively identical at the lac promoter and other class I CAP-dependent promoters, but are different at a class II CAP-dependent promoter. We propose that the surface loop consisting of residues 152 to 166 makes identical molecular interactions in transcription activation at all class I CAP-dependent promoters, irrespective of distance between the DNA site for CAP and the transcription start point, but makes a different set of molecular interactions in transcription activation at class II CAP-dependent promoters.
依赖于CAP的启动子可根据CAP的DNA结合位点的位置分为不同类别。在I类依赖于CAP的启动子中，CAP的DNA结合位点位于聚合酶的DNA结合位点上游；只要CAP的DNA结合位点和RNA聚合酶的DNA结合位点位于DNA螺旋的同一面上，CAP的DNA结合位点可位于距转录起始点不同的距离处。在II类依赖于CAP的启动子中，CAP的DNA结合位点与RNA聚合酶的DNA结合位点重叠，取代了RNA聚合酶结合的-35决定簇。在先前的工作中，我们已经表明，由CAP的氨基酸残基152至166组成的表面环对于在特征最明确的I类依赖于CAP的启动子即lac启动子上的转录激活至关重要，并且我们提出该表面环在lac启动子、CAP和RNA聚合酶的三元复合物中与RNA聚合酶进行直接的蛋白质-蛋白质接触。在此，我们表明由氨基酸残基152至166组成的表面环对于其他I类依赖于CAP的启动子和一个II类依赖于CAP的启动子上的转录激活至关重要。我们进一步表明，残基152至166的丙氨酸取代在lac启动子和其他I类依赖于CAP的启动子上的定性效应是相同的，但在一个II类依赖于CAP的启动子上是不同的。我们提出，由残基152至166组成的表面环在所有I类依赖于CAP的启动子的转录激活中进行相同的分子相互作用，而与CAP的DNA结合位点和转录起始点之间的距离无关，但在II类依赖于CAP的启动子的转录激活中进行不同组的分子相互作用。
