核糖体蛋白L6/Taxreb107的核定位信号的分析

核糖体蛋白L6（RpL6，Taxreb107）含有三个具有核定位信号特征的基序.用作者构建的核定位信号捕获系统分析了这些核定位信号是否具有介导蛋白质进行核转位的功能.将RpL6/Taxreb107分段插入核定位信号捕获载体的克隆位点后转化宿主酵母，发现其前两个核定位信号可以介导融合蛋白进入细胞核，而第三个核定位信号无此作用.将RpL6/Taxreb107分段与绿色荧光蛋白融合后转染培养的哺乳类细胞，证实了以上在酵母中所得的结果.进一步发现RpL6/Taxreb107的前两个核定位信号同时具有核仁定位的功能.当在细胞中表达的早期，进入核内的融合蛋白优先定位于核仁.这些结果一方面有助于理解RpL6/Taxreb107核转位的机理，同时说明作者构建的核定位信号捕获系统也可用在蛋白质中寻找核定位信号.

Analysis of Nuclear Localization Signal (NLS) in Ribosomal Protein L6/Taxreb107

Ribosomal protein L6 (RpL6, also called Taxreb107) possesses at least three nuclear localization signal (NLS)-like motifs. The activity of these motifs for their ability to mediate protein nuclear translocation was analyzed by using a NLS trapping system established. The full length or different fragments of RpL6/Taxreb107 cDNA was inserted to the cloning site of NLS trapping vector and the resulting constructs were used for transformation of host yeast. The result showed that the first two NLS-like motifs of RpL6/Taxreb107 induced the fusion protein to be transfected into the nucleus while the third one did not. This conclusion was confirmed by transfection of cultured cells with (EGFP) fused with different RpL6/Taxreb107 fragments. The results also showed that the first two NLS-like motifs of RpL6/Taxreb107 have nucleolus localization activity. When expressed in cultured cells, the RpL6/Taxreb107 fragments containing the first two NLS preferentially induced the fusion protein to be transfected into the nucleoli. These results are helpful for understanding of the nuclear translocation of RpL6/Taxreb107, and also confirmed that the NLS-trapping system is useful for searching NLS in proteins.