Hillel Z, Wu C W
Biochemistry. 1978 Jul 25;17(15):2954-61. doi: 10.1021/bi00608a003.
We have identified the subunits of Escherichia coli RNA polymerase which are in close contact with the T7 phage DNA template using photochemical cross-linking. In nonspecific T7 DNA-enzyme complexes which occur in all regions of the DNA, subunits sigma, beta, and beta' were cross-linked to the DNA. In contrast, in specific binary complexes which presumably occur at promoter sites, and in the initiation complex (holoenzyme + T7 DNA + initiator dinucleotides + three nucleoside triphosphates), only sigma and beta were cross-linked to DNA, while cross-linking of beta' could not be demonstrated. These results (1) do not support the idea that alpha subunits are involved in the enzyme-template interaction, (2) raise the possibility that sigma subunit participates directly in promoter recognition even though isolated sigma does not bind to DNA, and (3) indicate different modes of interaction between RNA polymerase and DNA in nonspecific and specific complexes. These findings are relevant to the mechanism by which RNA polymerase carries out selective transcription.
我们利用光化学交联法鉴定了大肠杆菌RNA聚合酶中与T7噬菌体DNA模板紧密接触的亚基。在DNA所有区域都存在的非特异性T7 DNA - 酶复合物中，σ、β和β'亚基与DNA发生了交联。相比之下，在可能出现在启动子位点的特异性二元复合物以及起始复合物（全酶 + T7 DNA + 起始二核苷酸 + 三磷酸核苷）中，只有σ和β与DNA发生了交联，而β'的交联未得到证实。这些结果（1）不支持α亚基参与酶 - 模板相互作用的观点，（2）增加了σ亚基即使在分离状态下不与DNA结合也直接参与启动子识别的可能性，（3）表明RNA聚合酶与DNA在非特异性和特异性复合物中的相互作用模式不同。这些发现与RNA聚合酶进行选择性转录的机制相关。
