Department of Molecular and Cell Biology, Boston University Medical Campus, Boston, MA, 02118, USA.
Bioinformatics Program, Boston University, Boston, MA, 02215, USA.
Nat Commun. 2019 Jan 11;10(1):146. doi: 10.1038/s41467-018-08137-2.
In Trypanosoma brucei, most mitochondrial mRNAs undergo editing, and 3' adenylation and uridylation. The internal sequence changes and terminal extensions are coordinated: pre-editing addition of the short (A) tail protects the edited transcript against 3'-5' degradation, while post-editing A/U-tailing renders mRNA competent for translation. Participation of a poly(A) binding protein (PABP) in coupling of editing and 3' modification processes has been inferred, but its identity and mechanism of action remained elusive. We report identification of KPAF4, a pentatricopeptide repeat-containing PABP which sequesters the A-tail and impedes mRNA degradation. Conversely, KPAF4 inhibits uridylation of A-tailed transcripts and, therefore, premature A/U-tailing of partially-edited mRNAs. This quality check point likely prevents translation of incompletely edited mRNAs. We also find that RNA editing substrate binding complex (RESC) mediates the interaction between the 5' end-bound pyrophosphohydrolase MERS1 and 3' end-associated KPAF4 to enable mRNA circularization. This event appears to be critical for edited mRNA stability.
在布氏锥虫中，大多数线粒体 mRNA 经历编辑、3' 腺苷酸化和尿苷酸化。内部序列变化和末端延伸是协调的：编辑前添加短 (A) 尾可保护编辑转录本免受 3'-5' 降解，而编辑后 A/U 尾化使 mRNA 能够进行翻译。聚（A）结合蛋白（PABP）参与编辑和 3' 修饰过程的偶联已被推断，但它的身份和作用机制仍然难以捉摸。我们报告了 KPAF4 的鉴定，KPAF4 是一种含有五肽重复的 PABP，可隔离 A 尾并阻碍 mRNA 降解。相反，KPAF4 抑制 A 尾化的转录本的尿苷酸化，因此，部分编辑的 mRNA 的过早 A/U 尾化。这个质量检查点可能防止不完全编辑的 mRNA 的翻译。我们还发现，RNA 编辑底物结合复合物（RESC）介导 5' 端结合的焦磷酸水解酶 MERS1 和 3' 端相关的 KPAF4 之间的相互作用，以实现 mRNA 环化。这个事件似乎对编辑后的 mRNA 稳定性至关重要。
