Entamoebas have a mitochondrion-derived organelle called the crypton or mitosome
, while the giardial gene encoding a 60-kDa chaperonin appears to be endosymbiont-derived, but no organelle has been identified (Clark and Roger, 1995; Roger et al., 1998; Mai et al., 1999; Tovar et al., 1999; Ghosh et al., 2000).
Twin [CX.sub.9]C proteins were found to be conserved across the organisms included in the study, except for three obligate intercellular parasites that contain mitosomes
. The evolutionary conservation across organisms containing true mitochondria suggested that these [CX.sub.9]C proteins are important in mitochondrial function and, indeed, members of this family operate as subunits in complexes I and IV of the electron transport chain (ETC), as cytochrome c oxidase (COX) assembly factors, and they participate in mitochondrial protein import, structure, and function.