Required during biogenesis of c-type cytochromes (cytochrome c6 and cytochrome f) at the step of heme attachment. May interact with Ccs1. The initiator methionine is created by RNA editing. The nonsense codons at positions 238 and 239 are modified to sense codons. Belongs to the CcmF/CycK/Ccl1/NrfE/CcsA family.