Hsieh Yi-Ching, Tu Pei-Jung, Lee Ying-Yuan, Kuo Chun-Chen, Lin Yi-Chien, Wu Chi-Fang, Lin Jing-Jer
Institute of Biopharmaceutical Sciences, National Yang-Ming University, Shih-Pai, 112, Taipei, Taiwan, ROC.
Biochem J. 2007 Dec 15;408(3):387-93. doi: 10.1042/BJ20070968.
Imp4p is a component of U3 snoRNP (small nucleolar ribonucleoprotein) involved in the maturation of 18S rRNA. We have shown that Imp4p interacts with Cdc13p, a single-stranded telomere-binding protein involved in telomere maintenance. To understand the role of Imp4p in telomeres, we purified recombinant Imp4p protein and tested its binding activity towards telomeric DNA using electrophoretic mobility-shift assays. Our results showed that Imp4p bound specifically to single-stranded telomeric DNA in vitro. The interaction of Imp4p to telomeres in vivo was also demonstrated by chromatin immunoprecipitation experiments. Significantly, the binding of Imp4p to telomeres was not limited to yeast proteins, since the hImp4 (human Imp4) also bound to vertebrate single-stranded telomeric DNA. Thus we conclude that Imp4p is a novel telomeric DNA-binding protein that, in addition to its role in rRNA processing, might participate in telomere function.
Imp4p是U3小核仁核糖核蛋白（small nucleolar ribonucleoprotein, snoRNP）的一个组成部分，参与18S核糖体RNA（rRNA）的成熟过程。我们已经证明，Imp4p与Cdc13p相互作用，Cdc13p是一种参与端粒维持的单链端粒结合蛋白。为了了解Imp4p在端粒中的作用，我们纯化了重组Imp4p蛋白，并使用电泳迁移率变动分析（electrophoretic mobility-shift assays）测试了其与端粒DNA的结合活性。我们的结果表明，Imp4p在体外特异性结合单链端粒DNA。染色质免疫沉淀实验也证明了Imp4p在体内与端粒的相互作用。值得注意的是，Imp4p与端粒的结合并不局限于酵母蛋白，因为人源Imp4（hImp4）也能与脊椎动物的单链端粒DNA结合。因此，我们得出结论，Imp4p是一种新型的端粒DNA结合蛋白，除了其在rRNA加工中的作用外，可能还参与端粒功能。
