RAM function is dependent on Kapβ2-mediated nuclear entry
RAM function is dependent on Kapβ2-mediated nuclear entry
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DOI：
10.1042/bj20131359
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发表时间：
2014-02-01
影响因子：
4.1
通讯作者：
Cowling, Victoria H.
中科院分区：
文献类型：
--
作者：
Gonatopoulos-Pournatzis, Thomas;Cowling, Victoria H.
真核基因的表达依赖于通过添加7-甲基鸟苷帽修饰前体mRNA的第一个转录核苷酸。帽保护转录物免受核酸外切酶的影响，并募集介导转录延伸、加工和翻译起始的复合物。帽通过一系列反应合成，这些反应通过5'至5'三磷酸桥将7-甲基鸟苷连接至第一个转录的核苷酸。在哺乳动物中，帽合成由RNGTT（RNA鸟苷酰转移酶和5 '-磷酸酶）和RNMT（RNA鸟嘌呤-7甲基转移酶）的顺序作用催化，这些酶在转录的早期阶段被募集到RNA pol II（聚合酶II）。我们最近发现，哺乳动物帽甲基转移酶是一个异源二聚体组成的RNMT和RNMT激活亚基RAM（RNMT激活迷你蛋白）。RAM激活并稳定RNMT，因此对细胞帽甲基化和细胞活力至关重要。在本研究中，我们报告RNMT与RAM的N-末端45个氨基酸相互作用，RAM是最大RNMT激活所必需和足够的结构域。相比之下，该RAM域的较小分量足以稳定RNMT。RAM在细胞核中起作用，我们报道RAM的核输入依赖于PY核定位信号和Kap β 2（karyopherin β 2）核转运蛋白。
Eukaryotic gene expression is dependent on the modification of the first transcribed nucleotide of pre-mRNA by the addition of the 7-methylguanosine cap. The cap protects transcripts from exonucleases and recruits complexes which mediate transcription elongation, processing and translation initiation. The cap is synthesized by a series of reactions which link 7-methylguanosine to the first transcribed nucleotide via a 5' to 5' triphosphate bridge. In mammals, cap synthesis is catalysed by the sequential action of RNGTT (RNA guanylyltransferase and 5'-phosphatase) and RNMT (RNA guanine-7 methyltransferase), enzymes recruited to RNA pol II (polymerase II) during the early stages of transcription. We recently discovered that the mammalian cap methyltransferase is a heterodimer consisting of RNMT and the RNMT-activating subunit RAM (RNMT-activating mini-protein). RAM activates and stabilizes RNMT and thus is critical for cellular cap methylation and cell viability. In the present study we report that RNMT interacts with the N-terminal 45 amino acids of RAM, a domain necessary and sufficient for maximal RNMT activation. In contrast, smaller components of this RAM domain are sufficient to stabilize RNMT. RAM functions in the nucleus and we report that nuclear import of RAM is dependent on PY nuclear localization signals and Kap beta 2 (karyopherin beta 2) nuclear transport protein.