Binding of TFIIIA To type 1 Promoter

TFIIIA contains nine C2H2 zinc fingers (Arakawa et al., 1995). It binds to both the ICR region of the 5S RNA genes and to 5S RNA to form the 7S storage ribonucleoprotein particle (Pelham and Brown, 1980). Upon TFIIIA binding to the 5S gene, the TFIIIA zinc fingers are aligned over the length of the ICR with the C-terminal zinc fingers in proximity to the 5 end, and the N-terminal zinc fingers in proximity to the 3 end, of the ICR. Zinc fingers 1-3 contact the C block within the ICR and have been reported to contribute most of the binding energy of the full-length protein (Clemens et al., 1992). However, TFIIIA fragments containing zinc fingers 4-9 bind to the A block and intermediate element within the ICR with affinities close to those of the full-length protein. This and other observations suggest that simultaneous binding by all nine TFIIIA zinc fingers requires energetically unfavorable distortions within the DNA, the protein, or both (Kehres et al., 1997).

TFIIIA含有九个C2H2锌指结构（Arakawa等人，1995年）。该结构能够与5S RNA基因的ICR区域以及5S RNA结合，进而形成7S储存核糖核蛋白颗粒（Pelham和Brown，1980年）。当TFIIIA与5S基因结合时，其锌指结构沿着ICR的全长排列，其中C端锌指靠近5'端，而N端锌指靠近3'端。锌指1-3与ICR内的C块接触，并已被证实为全长度蛋白质结合能的主要贡献者（Clemens等人，1992年）。然而，含有锌指4-9的TFIIIA片段与ICR内的A块和中间元素结合，其亲和力接近全长度蛋白质。这一现象以及其他观察结果均表明，所有九个TFIIIA锌指的同时结合需要在DNA、蛋白质或两者之间产生能量上不利的形变（Kehres等人，1997年）。