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将转录与翻译分离的细胞核。根据此处提出的更新的病毒真核发生 (VE) 假说，真核细胞核来自感染真核生物古细菌祖先的 DNA 病毒的病毒工厂。VE 假设意味着细胞核的许多独特特征，包括真核细胞核将转录与翻译分离的机制，应该是病毒而不是细胞起源的。现代真核细胞核使用数百个协同作用的真核生物特异性基因的复杂过程将转录与翻译分离。这个复杂的过程是由真核生物 mRNA 上的真核生物特异性 7-甲基鸟苷酸 (m7G) 帽引发的，该帽靶向 mRNA 进行剪接、核输出、和细胞质翻译。此处显示真核 m7G 加帽装置的同源物存在于Mimiviridae显然一般不存在于古生菌中，特别是Lokiarchaeota，一种提议的真核生物的古菌亲属。m7G 加帽装置的系统发育分析表明，真核细胞核和拟杆菌科从一个共同的祖先来源获得这种共享途径，该来源早于最后的真核共同祖先 (LECA) 的起源。这些结果与真核细胞核和拟杆菌科从一种古老的病毒中获得这些能力的假设一致，这种病毒可以被认为是“第一真核细胞祖先”（FENA）。