Figure 2.

Scheme depicting an evolutionary hypothesis that explains genome locations of groEL and cpn60. An ancestral eubacterial-like groEL duplicated in cyanobacteria to give two homologues: groEL1 and groEL2. Both copies were inherited by phototrophic eukaryotes. One of the copies, groEL1, has been lost from the plastid genome in some lineages. groEL2 was transferred into the cell nucleus and gave rise to cpn60 in the case where groEL1 is still maintained in the plastid genome, or into cpn60α and cpn60β, where groEL1 has been deleted. For details see text. P.D. = predicted.