Required during biogenesis of c-type cytochromes (cytochrome c6 and cytochrome f) at the step of heme attachment. May interact with Ccs1. Met-1 is the initiator; however when Met-1 is mutated a low amount of protein may be produced, probably from Met-20. Belongs to the CcmF/CycK/Ccl1/NrfE/CcsA family.