Analysis by Engineering for Two DNA Binding Proteins That Regulate The Initiation of Ribosomal RNA Synthesis.

核糖体RNA基因（rDNA）转录起始复合物的形成需要上游结合蛋白（Upstream binding Protein， UBF）和SL-1两种DNA结合蛋白。小鼠UBF在第4个HMG-box中有一个核定位序列。HMG-box1 （rDNA结合的关键区域）或酸尾（可能与SL-1相互作用的区域）的缺失都会导致核核靶向的丧失。HMG-box1是UBF与rDNA上游控制元件结合所必需的。小鼠UBF通过其NLS转移到细胞核中，并通过hmg -box和酸性尾与rDNA启动子的特异性和稳定结合而被隔离在细胞核中。在转录起始位点和-1200nt之间的区域显示启动子活性。本地区有几种gc -box和三种血清反应要素，但没有TATA-box和CAT-box。这些顺式作用元件的存在是调控UBF基因的必要条件。营养上移后，UBF mRNA表达量增加了4倍。这些观察结果表明，UBF基因是一种看家基因，并通过启动子区域的几种元件与生长刺激信号相对应地进行调控。SL-1由5种蛋白组成，其中至少含有TATA结合蛋白（TBP）。UBF与TBP相关蛋白结合。抗TBP抗体可抑制体外核糖体RNA合成。TBP结合rDNA的启动子区域。然后UBF与SL-1/DNA复合物形成稳定的复合物，作为rDNA转录的起始前复合物。

It is necessary two DNA binding proteins, Upstream Binding Protein(UBF)and SL-1, for formation of the initiation complex of ribosomal RNA gene(rDNA)transcription. Mouse UBF has a nuclear localization sequence in the 4th HMG-box. Deletion of either the HMG-box1, a region crucial for rDNA binding, or the acidic tail, a region that may interasct with SL-1, results in the loss of necleolar targeting. HMG-box1 is necessary for UBF to bind to the upstream control element of the rDNA.Mouse UBF is transferred to the nucleus by its NLS and is sequestered in the nucleous by its specific and stable binding to the rDNA promoter via HMG-boxes and the acidic tail.The region between the transcriptional initiation site and -1200nt shows the promoter activities. In this region, there are several GC-boxes and three kinds of serum response elements, but no TATA-box or CAT-box. The existence of those cis acting element is necessary for regulation of the UBF gene. The mRNA of UBF was expressed 4 times after nutritional shift-up. These observation indicates UBF gene is one of the house-keeping genes and is regulated through several kinds of element in the promoter region correspondingly with growth-stimulation signals. SL-1 is constituted with 5 kinds of proteins, containing TATA binding protein(TBP), at least. UBF binds with protein associated TBP.Ribosomal RNA synthesis in vitro is inhibited with anti-body against TBP.So TBP binds the promoter region of rDNA.And then UBF makes a stable complex with SL-1/DNA complex as pre-initiation complex of rDNA transcription.