Novel and essential subunits in the 300-kilodalton nuclear cap binding complex of Trypanosoma brucei
Novel and essential subunits in the 300-kilodalton nuclear cap binding complex of Trypanosoma brucei
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DOI：
10.1128/mcb.25.6.2216-2226.2005
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发表时间：
2005-03-01
影响因子：
5.3
通讯作者：
Tschudi, C
中科院分区：
文献类型：
--
作者：
Li, HJ;Tschudi, C
锥虫原虫RNA加工的一个独特方面是在所有mRNAs的5‘端存在一个帽4结构(M(7)Gpppm(2)(6)AmpAmpCmpm(3)Um)。帽4通过对剪接的前导RNA提供的39个核苷酸长的序列的反式剪接成为mRNA的一部分。虽然4帽的修饰是发生反式剪接所必需的，但其潜在的机制仍有待确定。我们现在描述了布氏锥虫中一个非常规的核帽结合复合体(CBC)，其表观分子质量为300 kDa，由五个蛋白质组分组成：已知的CBC亚基CBP20和Importin-α，以及三个新的蛋白质，这些蛋白质只存在于具有Cap4结构和反式剪接的生物体中。竞争结合研究与CBC和Cap4结构之间的特定相互作用是一致的。通过RNA干扰下调布氏毛滴虫CBC的几个单独成分，在反式剪接的早期阶段证明了一个重要的功能。因此，我们的研究与CBC在CAP4修饰和反式剪接之间提供了机械联系是一致的。
One of the unique aspects of RNA processing in trypanosomatid protozoa is the presence of a cap 4 structure (M(7)Gpppm(2)(6)AmpAmpCmpm(3)Um) at the 5' end of all mRNAs. The cap 4 becomes part of the mRNA through trans-splicing of a 39-nucleotide-long sequence donated by the spliced leader RNA. Although the cap 4 modifications are required for trans-splicing to occur, the underlying mechanism remains to be determined. We now describe an unconventional nuclear cap binding complex (CBC) in Trypanosoma brucei with an apparent molecular mass of 300 kDa and consisting of five protein components: the known CBC subunits CBP20 and importin-alpha and three novel proteins that are only present in organisms featuring a cap 4 structure and trans-splicing. Competitive binding studies are consistent with a specific interaction between the CBC and the cap 4 structure. Downregulation of several individual components of the T. brucei CBC by RNA interference demonstrated an essential function at an early step in trans-splicing. Thus, our studies are consistent with the CBC providing a mechanistic link between cap 4 modifications and trans-splicing.