Reynolds W F, Gottesfeld J M
Proc Natl Acad Sci U S A. 1983 Apr;80(7):1862-6. doi: 10.1073/pnas.80.7.1862.
Relaxation of Xenopus 5S plasmid DNA (pX1o8) in the presence of transcription factor (TF) IIIA reduces the linking number of the DNA. Parallel experiments with plasmid pMB9 or cloned hepatitis B viral DNA indicate a degree of non-specific unwinding by TF; however, 60% of the effect observed for pX1o8 is due to specific interaction of TF IIIA with the 5S rRNA gene internal promoter sequence. The extent of unwinding (0.2-0.4 helical turn per TF IIIA binding site) is not consistent with the complete denaturation of the 50-base-pair TF binding site; however, it is consistent with a change in helix rotation, denaturation of 2-4 nucleotides per binding site, or DNA wrapping about a protein core. We show that proteins other than TF IIIA (bovine serum albumin and RNase) have no effect on the linking number of DNA when present during relaxation and that the unwinding activity associated with TF is heat labile. These results suggest that TF IIIA may facilitate transcription by altering the helical configuration of 5S DNA.
在转录因子（TF）IIIA存在的情况下，非洲爪蟾5S质粒DNA（pX1o8）的松弛会降低DNA的连环数。用质粒pMB9或克隆的乙型肝炎病毒DNA进行的平行实验表明，TF存在一定程度的非特异性解旋；然而，观察到的pX1o8效应的60%是由于TFIIIA与5S rRNA基因内部启动子序列的特异性相互作用。解旋程度（每个TFIIIA结合位点0.2 - 0.4个螺旋圈）与50个碱基对的TF结合位点的完全变性不一致；然而，它与螺旋旋转的变化、每个结合位点2 - 4个核苷酸的变性或DNA围绕蛋白质核心的缠绕是一致的。我们表明，在松弛过程中存在时，除TFIIIA之外的蛋白质（牛血清白蛋白和核糖核酸酶）对DNA的连环数没有影响，并且与TF相关的解旋活性对热不稳定。这些结果表明，TFIIIA可能通过改变5S DNA的螺旋构型来促进转录。
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