Conservation of a masked nuclear export activity of La proteins and its effects on tRNA maturation
Conservation of a masked nuclear export activity of La proteins and its effects on tRNA maturation
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DOI：
10.1128/mcb.00026-07
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发表时间：
2007-05-01
影响因子：
5.3
通讯作者：
Maraia, Richard J.
中科院分区：
文献类型：
--
作者：
Bayfield, Mark A.;Kaiser, Trish E.;Maraia, Richard J.
La是一种与RNA加工相关的磷蛋白，其高度保守，以至于人类La蛋白（hLa）在体内能够替代裂殖酵母La蛋白（Sla1p）的tRNA加工功能。La蛋白包含多个运输元件，这些元件支持其在不同亚细胞位置与RNAs相互作用。先前的数据表明，在裂殖酵母中，核滞留元件（NRE）的缺失会导致La的核输出以及相关前体tRNAs的加工功能失调，这些前体tRNAs虽已被剪接，但5'和3'端未加工，同时伴有tRNA介导的抑制作用降低。为了进一步探究这些观察结果，我们首先鉴定了hLa和Sla1p的NRE中的保守残基，当这些残基被替换时，会模拟NRE缺失的表型。然后，对其他基序缺失的NRE缺陷型La蛋白的研究表明，RNA识别基序I（RRM1）是核输出所必需的。对保守的RRM1残基进行突变可恢复NRE缺陷型La蛋白的核积累。一些RRM1突变恢复了核积累，防止了前体tRNA加工紊乱，并恢复了抑制作用，这表明RRM1的tRNA相关活性及其核输出活性在功能上是可分离的。当映射到hLa结构上时，对输出敏感的残基所构成的表面与RRM1的RNA结合表面不同。数据表明，NRE是保守的，用于掩盖或在功能上超越RRM1同样保守的核输出活性。数据提示，保守元件介导多功能La蛋白的核滞留、核输出和RNA结合活性，并且它们之间的相互关系有助于La在不同细胞位置与不同类别的RNA配体结合的能力。
La is an RNA-processing-associated phosphoprotein so highly conserved that the human La protein (hLa) can replace the tRNA-processing function of the fission yeast La protein (Sla1p) in vivo. La proteins contain multiple trafficking elements that support interactions with RNAs in different subcellular locations. Prior data indicate that deletion of a nuclear retention element (NRE) causes nuclear export of La and dysfunctional processing of associated pre-tRNAs that are spliced but 5' and 3' unprocessed, with an accompanying decrease in tRNA-mediated suppression, in fission yeast. To further pursue these observations, we first identified conserved residues in the NREs of hLa and Sla1p that when substituted mimic the NRE deletion phenotype. NRE-defective La proteins then deleted of other motifs indicated that RNA recognition motif I (RRM1) is required for nuclear export. Mutations of conserved RRM1 residues restored nuclear accumulation of NRE-defective La proteins. Some RRM1 mutations restored nuclear accumulation, prevented disordered pre-tRNA processing, and restored suppression, indicating that the tRNA-related activity of RRM1 and its nuclear export activity could be functionally separated. When mapped onto an hLa structure, the export-sensitive residues comprised surfaces distinct from the RNA-binding surface of RRM1 The data indicate that the NRE has been conserved to mask or functionally override an equally conserved nuclear export activity of RRM1 The data suggest that conserved elements mediate nuclear retention, nuclear export, and RNA-binding activities of the multifunctional La protein and that their interrelationship contributes to the ability of La to engage its different classes of RNA ligands in different cellular locations.