A Los1p-independent pathway for nuclear export of intronless tRNAs in Saccharomyces cerevisiae
A Los1p-independent pathway for nuclear export of intronless tRNAs in Saccharomyces cerevisiae
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DOI：
10.1073/pnas.082682699
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发表时间：
2002-04-16
影响因子：
11.1
通讯作者：
Hopper, AK
中科院分区：
文献类型：
--
作者：
Feng, WQ;Hopper, AK
Los1p 是酿酒酵母的输出蛋白-t 同源物，可结合 tRNA，并在前 tRNA 剪接和将成熟 tRNA 从细胞核输出到细胞质中发挥作用。由于 LOS1 在酵母中不是必需的，因此必须存在其他 tRNA 核输出途径。我们报道，Cca1p 在 tRNA 的 3' 末端添加核苷酸 C、C 和 A，是由 los1 无效突变引起的 tRNA 核输出缺陷的多拷贝抑制因子。 Mes1p（甲硫氨酰-tRNA 合成酶）还可抑制 los1 细胞中 tRNA(Met) 核输出的缺陷。因此，Cca1p 和 Mes1p 似乎在不依赖于 Los1p 的 tRNA 核输出途径中发挥作用。异核体分析表明 Cca1p 是一种细胞核/细胞质穿梭蛋白，这为 Cca1p 在该 tRNA 核输出途径中充当输出蛋白或衔接子提供了潜力。在酵母中，大多数影响 tRNA 核输出的突变也会导致前 tRNA 剪接缺陷，导致剪接和输出过程紧密耦合。相比之下，我们发现过表达的 Cca1p 可以纠正 los1::Kan(r) 细胞的核输出，但不能纠正 los1::Kan(r) 细胞的前 tRNA 剪接缺陷，从而解开前 tRNA 剪接和 tRNA 核输出。
Los1p, the Saccharomyces cerevisiae exportin-t homologue, binds tRNA and functions in pre-tRNA splicing and export of mature tRNA from the nucleus to the cytosol. Because LOS1 is unessential in yeast, other pathways for tRNA nuclear export must exist. We report that Cca1p, which adds nucleotides C, C, and A to the 3' end of tRNAs, is a multicopy suppressor of the defect in tRNA nuclear export caused by los1 null mutations. Mes1p, methionyl-tRNA synthetase, also suppresses the defect in nuclear export of tRNA(Met) in los1 cells. Thus, Cca1p and Mes1p seem to function in a Los1p-independent tRNA nuclear export pathway. Heterokaryon analysis indicates that Cca1p is a nucleus/cytosol-shuttling protein, providing the potential for Cca1p to function as an exporter or an adapter in this tRNA nuclear export pathway. In yeast, most mutations that affect tRNA nuclear export also cause defects in pre-tRNA splicing leading to tight coupling of the splicing and export processes. In contrast, we show that overexpressed Cca1p corrects the nuclear export, but not the pre-tRNA-splicing defects of los1::Kan(r) cells, thereby uncoupling pre-tRNA splicing and tRNA nuclear export.