 The first model known as the " syntrophic model " proposes that a symbiotic relationship between the archaea and bacteria created the nucleus @-@ containing eukaryotic cell . ( Organisms of the Archaea and Bacteria domain have no cell nucleus . ) It is hypothesized that the symbiosis originated when ancient archaea , similar to modern methanogenic archaea , invaded and lived within bacteria similar to modern myxobacteria , eventually forming the early nucleus . This theory is analogous to the accepted theory for the origin of eukaryotic mitochondria and chloroplasts , which are thought to have developed from a similar endosymbiotic relationship between proto @-@ eukaryotes and aerobic bacteria . The archaeal origin of the nucleus is supported by observations that archaea and eukarya have similar genes for certain proteins , including histones . Observations that myxobacteria are motile , can form multicellular complexes , and possess kinases and G proteins similar to eukarya , support a bacterial origin for the eukaryotic cell . 
