Cofactor maturation pathways such as the CCB system (system IV) for cytochrome c-heme attachment are conserved in all organisms performing oxygenic photosynthesis [1]. The CCB system consists of four proteins: CCB1-4. CCB2 and CCB4 are paralogues derived from a unique cyanobacterial ancestor [1]. Orthologues are conserved in higher plants [2].

1: A specific c-type cytochrome maturation system is required for oxygenic photosynthesis. Kuras R, Saint-Marcoux D, Wollman FA, de Vitry C; Proc Natl Acad Sci U S A. 2007;104:9906-9910. PMID:17535914

2: A novel pathway of cytochrome c biogenesis is involved in the assembly of the cytochrome b6f complex in arabidopsis chloroplasts. Lezhneva L, Kuras R, Ephritikhine G, de Vitry C; J Biol Chem. 2008;283:24608-24616. PMID:18593701