viral eukaryogenesis

Viral eukaryogenesis is the hypothesis that the cell nucleus of eukaryotic life forms evolved from a large DNA virus in a form of endosymbiosis within a methanogenic archaeon or a bacterium. The virus later evolved into the eukaryotic nucleus by acquiring genes from the host genome and eventually usurping its role. The hypothesis was first proposed by Philip Bell in 2001 and was further popularized with the discovery of large, complex DNA viruses (such as Mimivirus) that are capable of protein biosynthesis. Viral eukaryogenesis has been controversial for several reasons. For one, it is sometimes argued that the posited evidence for the viral origins of the nucleus can be conversely used to suggest the nuclear origins of some viruses. Secondly, this hypothesis has further inflamed the longstanding debate over whether viruses are living organisms. Hypothesis The viral eukaryogenesis hypothesis posits that eukaryotes are composed of three ancestral elements: a viral component that became the modern nucleus; a prokaryotic cell (an archaeon according to the eocyte hypothesis) which donated the cytoplasm and cell membrane of modern cells; and another prokaryotic cell (here bacterium) that, by endocytosis, became the modern mitochondrion or chloroplast.