Clos J, Buttgereit D, Grummt I
Proc Natl Acad Sci U S A. 1986 Feb;83(3):604-8. doi: 10.1073/pnas.83.3.604.
A transcription factor that is specific for mouse rDNA has been partially purified from Ehrlich ascites cells. This factor [designated transcription initiation factor (TIF)-IB] is required for accurate in vitro synthesis of mouse rRNA in addition to RNA polymerase I and another regulatory factor, TIF-IA. TIF-IB activity is present in extracts both from growing and nongrowing cells in comparable amounts. Prebinding competition experiments with wild-type and mutant templates suggest that TIF-IB interacts with the core control element of the rDNA promoter, which is located immediately upstream of the initiation site. The specific binding of TIF-IB to the RNA polymerase I promoter is demonstrated by exonuclease III protection experiments. The 3' border of the sequences protected by TIF-IB is shown to be on the coding strand at position -21 and on the noncoding strand at position -7. The results suggest that direct binding of TIF-IB to sequences in the core promoter element is the mechanism by which this factor imparts promoter selectivity to RNA polymerase I.
一种对小鼠核糖体DNA（rDNA）具有特异性的转录因子已从艾氏腹水细胞中部分纯化出来。除了RNA聚合酶I和另一种调节因子TIF-IA外，该因子[命名为转录起始因子（TIF）-IB]是小鼠rRNA体外精确合成所必需的。TIF-IB活性在生长细胞和非生长细胞的提取物中含量相当。用野生型和突变型模板进行的预结合竞争实验表明，TIF-IB与rDNA启动子的核心控制元件相互作用，该元件位于起始位点的紧邻上游。外切核酸酶III保护实验证明了TIF-IB与RNA聚合酶I启动子的特异性结合。TIF-IB保护的序列的3'边界显示在编码链上的-21位和非编码链上的-7位。结果表明，TIF-IB与核心启动子元件中的序列直接结合是该因子赋予RNA聚合酶I启动子选择性的机制。
