Fig. 1.

A scenario for the origin of modern compartmentalized cells (Eukarya and PVC bacteria) from a compartmentalized LUCA. A, Archaea; B, Bacteria; E, Eukarya. The cytoplasm and chromosomes of Archaea and Eukarya are shown with the same color in reference to the high similarity of these two domains for informational proteins and several membrane-bound processes (e.g., ATP synthesis). For the sake of simplicity, eukaryotic organelles have not been indicated. Also for simplicity, the ICM of PVC bacteria and the ER of Eukarya have been schematically drawn as intracellular circles. The horizontal black bars indicate loss of MC proteins. NM, nuclear membrane.