Microbiogen Pty Ltd, Unit E2, Lane Cove Business Park, Lane Cove West, NSW, 2066, Australia.
Virus Res. 2020 Nov;289:198168. doi: 10.1016/j.virusres.2020.198168. Epub 2020 Sep 20.
The defining feature of the eukaryotic cell is the possession of a nucleus that uncouples transcription from translation. According to the updated Viral Eukaryogenesis (VE) hypothesis presented here, the eukaryotic nucleus descends from the viral factory of a DNA virus that infected the archaeal ancestor of the eukaryotes. The VE hypothesis implies that many unique features of the nucleus, including the mechanisms by which the eukaryotic nucleus uncouples transcription from translation, should be viral rather than cellular in origin. The modern eukaryotic nucleus uncouples transcription from translation using a complex process employing hundreds of eukaryotic specific genes acting in concert. This intricate process is primed by the eukaryote specific 7-methylguanylate (m7G) cap on eukaryotic mRNA that targets mRNA for splicing, nuclear export, and cytoplasmic translation. It is shown here that homologues of the eukaryotic m7G capping apparatus are present in viruses of the Mimiviridae yet are apparently absent from archaea generally, and specifically from Lokiarchaeota, a proposed archaeal relative of the eukaryotes. Phylogenetic analysis of the m7G capping apparatus shows that eukaryotic nuclei and Mimiviridae obtained this shared pathway from a common ancestral source that predated the origin of the Last Eukaryotic Common Ancestor (LECA). These results are consistent with the hypothesis that the eukaryotic nucleus and the Mimiviridae obtained these abilities from an ancient virus that could be considered the 'First Eukaryotic Nuclear Ancestor' (FENA).
真核细胞的定义特征是拥有一个核，使转录与翻译解耦。根据这里提出的更新的病毒真核起源（VE）假说，真核核是从感染真核生物祖先的 DNA 病毒的病毒工厂演化而来的。VE 假说意味着，许多核的独特特征，包括真核核使转录与翻译解耦的机制，应该是病毒起源而不是细胞起源。现代真核核使用一个复杂的过程来使转录与翻译解耦，该过程涉及数百个协同作用的真核特异性基因。这个复杂的过程是由真核生物特有的 7-甲基鸟苷（m7G）帽在真核 mRNA 上引发的，该帽靶向 mRNA 进行剪接、核输出和细胞质翻译。这里表明，Mimiviridae 病毒中存在真核 m7G 加帽装置的同源物，但通常在古菌中，特别是在 Lokiarchaeota 中显然不存在，后者被认为是真核生物的一个假定的古菌亲属。m7G 加帽装置的系统发育分析表明，真核核和 Mimiviridae 从一个共同的祖先来源获得了这个共享途径，这个祖先来源早于最后一个真核生物共同祖先（LECA）的起源。这些结果与假说一致，即真核核和 Mimiviridae 从一个可以被认为是“第一个真核核祖先”（FENA）的古老病毒中获得了这些能力。
