The hypothesized ancestor of eukaryotes. As outlined in the diagram, this organism arose by fusion of two prokaryotes with complementing metabolic capabilities. The first had a fragmented RNA-based genome that encoded the RNAs functioning in translation and the elaboration of cytoskeletal proteins. Once equipped with a cytoskeleton, the prokaryote could engulf other microorganisms. The second organism was a primitive archeon with a relatively unfragmented DNA genome that encoded metabolically active proteins. The first organism engulfed the second, which eventually functioned as the nucleus in the chimera. See Chronology, 1991, Sogin; serial symbiosis theory.
Sogin's first symbiont. Adapted from Current Opinion in Genetics and Development Vol. 1, M. L. Sogin, Early evolution and the origin of eukaryotes, pp. 457–463. © 1991, reproduced with permission from Elsevier and from M. L. Sogin.
Subjects: Genetics and Genomics.