The genome sequence of the microorganism Methanococcus jannaschii confirmed that there is a third main branch of life on Earth, along with prokaryotes (bacteria) and eukaryotes (fungi, protists, plants, and animals). The third branch is called Archaea. The group includes a diverse array of small cells that lack nuclei, like bacteria, but are genetically and evolutionarily distinct from bacteria. Preliminary comparisons between M. jannaschii and two completed bacterial (i.e. prokaryotic) genomes indicated that M. jannaschii has a large number of genes that are unlike any seen before.
Last Reviewed: May 9, 2013