Liker E, Fernandez E, Izaurralde E, Conti E
European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, D-69117 Heidelberg, Germany.
EMBO J. 2000 Nov 1;19(21):5587-98. doi: 10.1093/emboj/19.21.5587.
Human TAP is implicated in mRNA nuclear export and is used by simian type D retroviruses to export their unspliced genomic RNA to the cytoplasm of the host cell. We have determined the crystal structure of the minimal TAP fragment that binds the constitutive transport element (CTE) of retroviral RNAs. Unexpectedly, we find the fragment consists of a ribonucleoprotein (RNP) domain, which is not identifiable by its sequence, and a leucine-rich repeat (LRR) domain. The non-canonical RNP domain functions as the general RNA-binding portion of the fragment. The LRR domain is required in cis to the RNP domain for CTE RNA binding. The structural and biochemical properties of the domains point to a remarkable similarity with the U2B"(RNP)-U2A'(LRR) spliceosomal heterodimer. Our in vitro and in vivo functional studies using structure-based mutants suggest that a phylogenetically conserved surface of the LRR domain of TAP may have different roles in the export of viral and cellular RNAs.
人TAP与mRNA的核输出有关，并且被猿猴D型逆转录病毒用于将其未剪接的基因组RNA输出到宿主细胞的细胞质中。我们已经确定了与逆转录病毒RNA的组成型转运元件（CTE）结合的最小TAP片段的晶体结构。出乎意料的是，我们发现该片段由一个无法通过其序列识别的核糖核蛋白（RNP）结构域和一个富含亮氨酸的重复（LRR）结构域组成。非典型RNP结构域作为该片段的一般RNA结合部分发挥作用。LRR结构域对于CTE RNA结合而言，在顺式方向上相对于RNP结构域是必需的。这些结构域的结构和生化特性表明，它们与U2B”（RNP）-U2A’（LRR）剪接体异二聚体具有显著的相似性。我们使用基于结构的突变体进行的体外和体内功能研究表明，TAP的LRR结构域在系统发育上保守的表面可能在病毒和细胞RNA的输出中具有不同的作用。
