 The most controversial model , known as viral <unk> , posits that the membrane @-@ bound nucleus , along with other eukaryotic features , originated from the infection of a <unk> by a virus . The suggestion is based on similarities between eukaryotes and viruses such as linear DNA strands , mRNA capping , and tight binding to proteins ( <unk> histones to viral <unk> ) . One version of the proposal suggests that the nucleus evolved in concert with <unk> to form an early cellular " predator " . Another variant proposes that eukaryotes originated from early archaea infected by <unk> , on the basis of observed similarity between the DNA <unk> in modern <unk> and eukaryotes . It has been suggested that the unresolved question of the evolution of sex could be related to the viral <unk> hypothesis . 
