The origin of the eukaryotic cell.

Molecular sequence data are beginning to provide important insights into the evolutionary origin of eukaryotic cells. Global phylogenies of numerous protein sequences indicate that the eukaryotic cell nucleus is a chimera, which has received major contributions from both a Gram-negative eubacterium and an archaebacterium. Recent studies also indicate that the formation of the nuclear envelope and the endoplasmic reticulum was accompanied by duplication of genes for the molecular chaperone proteins (e.g. hsp70, hsp90), which facilitate protein transport across membranes. Based on these observations, it is suggested that the ancestral eukaryotic cell arose by a unique endosymbiotic event involving engulfment of an eocyte archaebacterium by a Gram-negative eubacterial host.