Ancient, highly conserved proteins from a LUCA with complex cell biology provide evidence in support of the nuclear compartment commonality (NuCom) hypothesis.

The nuclear compartment commonality (NuCom) hypothesis posits a complex last common ancestor (LUCA) with membranous compartments including a nuclear membrane. Such a LUCA then evolved to produce two nucleated lineages of the tree of life: the Planctomycetes-Verrucomicrobia-Chlamydia superphylum (PVC) within the Bacteria, and the Eukarya. We propose that a group of ancient essential protokaryotic signature proteins (PSPs) originating in LUCA were incorporated into ancestors of PVC Bacteria and Eukarya. Tubulins, ubiquitin system enzymes and sterol-synthesizing enzymes are consistent with early origins of these features shared between the PVC superphylum and Eukarya.