 Based on parsimony @-@ based phylogenetic analysis , the most recent common ancestor of all eukaryotes most likely already possessed an early RNA interference pathway ; the absence of the pathway in certain eukaryotes is thought to be a derived characteristic . This ancestral RNAi system probably contained at least one dicer @-@ like protein , one argonaute , one <unk> protein , and an RNA @-@ dependent RNA polymerase that may also have played other cellular roles . A large @-@ scale comparative genomics study likewise indicates that the eukaryotic crown group already possessed these components , which may then have had closer functional associations with generalized RNA degradation systems such as the exosome . This study also suggests that the RNA @-@ binding argonaute protein family , which is shared among eukaryotes , most archaea , and at least some bacteria ( such as <unk> <unk> ) , is homologous to and originally evolved from components of the translation initiation system . 
