在轉(zhuǎn)錄和處理之后，轉(zhuǎn)移RNA（tRNA）被從細胞核輸出到細胞質(zhì)中,，在那里發(fā)生轉(zhuǎn)錄。tRNA被一個名為Xpo-t的運輸因子攜帶穿過核膜中的小孔?，F(xiàn)在,，Xpo-t的結(jié)構已被確定。其結(jié)構是在單獨情況下和與tRNA及運輸所需要的另一個因子Ran-GTP結(jié)合的情況下分別被確定的,。與tRNA的結(jié)合誘導大的構形變化,，從而使得Xpo-t將tRNA包圍起來，并與其5'端和3'端都發(fā)生相互作用,。這可解釋蛋白合成中質(zhì)量控制的一個重要機制,，按照該機制，具有未成熟端的未被處理的tRNA被阻止,，而不能從細胞核中被運送出去,。（生物谷Bioon.com）
生物谷推薦原始出處：
Nature 461, 60-65 (3 September 2009) | doi:10.1038/nature08394
Structures of the tRNA export factor in the nuclear and cytosolic statesnear-final version
Atlanta G. Cook1, Noemi Fukuhara2,3, Martin Jinek2,3 & Elena Conti1,2
1 Structural Cell Biology, MPI for Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
2 EMBL, Meyerhofstrasse 1, Heidelberg D69117, Germany
3 Present addresses: Division of Cell and Molecular Biology, Biophysics section, Blackett Laboratory, Imperial College London, London SW7 2AZ, UK (N.F.); Department of Molecular Cell Biology, University of California at Berkeley, 731 Stanley Hall, Berkeley, California 94720, USA (M.J.).
Transfer RNAs are among the most ubiquitous molecules in cells, central to decoding information from messenger RNAs on translating ribosomes. In eukaryotic cells, tRNAs are actively transported from their site of synthesis in the nucleus to their site of function in the cytosol. This is mediated by a dedicated nucleo-cytoplasmic transport factor of the karyopherin- family (Xpot, also known as Los1 in Saccharomyces cerevisiae). Here we report the 3.2 ? resolution structure of Schizosaccharomyces pombe Xpot in complex with tRNA and RanGTP, and the 3.1 ? structure of unbound Xpot, revealing both nuclear and cytosolic snapshots of this transport factor. Xpot undergoes a large conformational change on binding cargo, wrapping around the tRNA and, in particular, binding to the tRNA 5' and 3' ends. The binding mode explains how Xpot can recognize all mature tRNAs in the cell and yet distinguish them from those that have not been properly processed, thus coupling tRNA export to quality control.
