THE ORIGIN OF THE EUKARYOTIC CELL

Molecular sequence data are beginning to provide important insights in to the evolutionary origin of eukaryotic cells. Global phylogenies of numerous protein sequences indicate that the eukaryotic cell nucleus i s a chimera, which has received major contributions from both a Gram-n egative eubacterium and an archaebacterium. Recent studies also indica te that the formation of the nuclear envelope and the endoplasmic reti culum was accompanied by duplication of genes for the molecular chaper one proteins (e.g. hsp70, hsp90), which facilitate protein transport a cross membranes. Based on these observations, it is suggested that the ancestral eukaryotic cell arose by a unique endosymbiotic event invol ving engulfment of an eocyte archaebacterium by a Gram-negative eubact erial host.