Niederberger N, Trachsel H, Altmann M
Institute for Biochemistry and Molecular Biology, University of Berne, Switzerland.
RNA. 1998 Oct;4(10):1259-67. doi: 10.1017/s1355838298980487.
The Saccharomyces cerevisiae TIF3 gene encodes a 436-amino acid (aa) protein that is the yeast homologue of mammalian translation Initiation factor eIF4B. Tif3p can be divided into three parts, the N-terminal region with an RNA recognition motif (RRM) (aa 1-182), followed in the middle part by a sevenfold repeat of 26 amino acids rich in basic and acidic residues (as 183-350), and a C-terminal region without homology to any known sequence (aa 351-436). We have analyzed several Tif3 proteins with deletions at their N and C termini for their ability (1) to complement a tif3delta strain in vivo, (2) to stimulate Tif3-dependent translation extracts, (3) to bind to single-stranded RNA, and (4) to catalyze RNA strand-exchange in vitro. Here we report that yeast Tif3/eIF4B contains at least two RNA binding domains able to bind to single-stranded RNA. One is located in the N-terminal region of the protein carrying the RRM, the other in the C-terminal two-thirds region of Tif3p. The RRM-containing domain and three of the seven repeat motifs are essential for RNA strand-exchange activity of Tif3p and translation in vitro and for complementation of a tif3delta strain, suggesting an important role for RNA strand-exchange activity in translation.
酿酒酵母TIF3基因编码一种436个氨基酸（aa）的蛋白质，它是哺乳动物翻译起始因子eIF4B的酵母同源物。Tif3p可分为三个部分，N端区域带有一个RNA识别基序（RRM）（第1 - 182个氨基酸），中间部分是富含碱性和酸性残基的26个氨基酸的七次重复序列（第183 - 350个氨基酸），C端区域与任何已知序列均无同源性（第351 - 436个氨基酸）。我们分析了几种在N端和C端有缺失的Tif3蛋白，检测它们的以下能力：（1）在体内互补tif3δ菌株；（2）刺激依赖Tif3的翻译提取物；（3）结合单链RNA；（4）在体外催化RNA链交换。在此我们报告，酵母Tif3/eIF4B含有至少两个能够结合单链RNA的RNA结合结构域。一个位于携带RRM的蛋白质的N端区域，另一个位于Tif3p的C端三分之二区域。含RRM的结构域和七个重复基序中的三个对于Tif3p的RNA链交换活性、体外翻译以及tif3δ菌株的互补是必需的，这表明RNA链交换活性在翻译中起重要作用。
