HISTORY ASSIGNMENT - WHEN WAS THE MITOCHONDRION FOUND

The near simultaneous radiation of the major eukaryotic evolutionary a ssemblages - plants, animals, fungi, and at least three other complex protist assemblages worthy of 'kingdom level' status - was preceded by the divergence of many independent protist lineages. The earliest bra nches are represented by organisms that do not contain mitochondria or plastids, suggesting that the primitive eukaryotic state did not incl ude these organelles. New information about nuclear-coded proteins tha t localize in the mitochondrion, however, suggests that the ancestral symbionts for mitochondria were present in the first eukaryotes. Phylo genetic support for this hypothesis is persuasive but it is not possib le to account for the relative times of divergence for mitochondria an d their ancestral symbionts relative to eukaryotic branching patterns inferred from nuclear genes. (C) Current Biology Ltd ISSN 0959-437X.