Neomura

Neomura (from Ancient Greek neo- "new", and Latin -murus "wall") is a proposed clade of life composed of the two domains Archaea and Eukaryota, coined by Thomas Cavalier-Smith in 2002. Its name reflects the hypothesis that both archaea and eukaryotes evolved out of the domain Bacteria, and one of the major changes was the replacement of the bacterial peptidoglycan cell walls with other glycoproteins. As of October 2024, the neomuran hypothesis is not accepted by most scientific workers; many molecular phylogenies suggest that eukaryotes are most closely related to one group of archaeans and evolved from them, rather than forming a clade with all archaeans, and that archaea and bacteria are sister groups both descended from the last universal common ancestor (LUCA). Other scenarios have been proposed based on competing phylogenies, and the relationship between the three domains of life (Archaea, Bacteria, and Eukaryota) was described in 2021 as "one of Biology's greatest mysteries". Considered as comprising the Archaea and the Eukaryota, the Neomura are a very diverse group, containing all of the multicellular species, as well as all of the most extremophilic species, but they all share certain molecular characteristics. All neomurans have histones to help with chromosome packaging, and most have introns. All use the molecule methionine as the initiator amino acid for protein synthesis (bacteria use formylmethionine). Finally, all neomurans use several kinds of RNA polymerase, whereas bacteria use only one. There are several hypotheses for the phylogenetic relationships between archaeans and eukaryotes. When Carl Woese first published his three-domain system in 1990, it was believed that the domains Bacteria, Archaea, and Eukaryota were equally old and equally related on the tree of life.