New archaebacterial genes coding for redox proteins: implications for the evolution of aerobic metabolism

Archaebacterial respiratory chains are poorly understood at the molecular level. We have cloned and sequenced a cluster of five new genes from the archaebacterium Sulfolobus acidocaldarius, four of them coding for redox proteins: a Rieske iron-sulphur protein, a cytochrome b, a subunit II of cytochrome oxidase and a blue copper protein (sulfocyanin). The fifth gene codes for a hydrophobic protein with no homologue in the databases. The gene organization and biochemical data suggest that all four redox proteins probably form part of a membrane respiratory complex together with SoxM, a previously characterized catalytic subunit of cytochrome oxidase. A phylogenetic analysis of the new protein sequences gives support to the view that an elaborate aerobic respiratory chain was already present in the last common ancestor of all living organisms.