May be required for the biogenesis of c-type cytochromes. Possible subunit of a heme lyase. Triple nrfE-nrfF-nrfG deletion mutants no longer attach heme 1 (covalently attached to 'Cys-122', the CWSCK motif) of cytochrome c552 (AC P0ABK9). Belongs to the CcmF/CycK/Ccl1/NrfE/CcsA family.