Pet191_N is the conserved N-terminal of a family of conserved proteins found from nematodes to humans. It carries six highly conserved cysteine residues. Pet191 is required for the assembly of active cytochrome c oxidase but does not form part of the final assembled complex [1].

1: Sequence and chromosomal localization of two PET genes required for cytochrome c oxidase assembly in Saccharomyces cerevisiae. McEwen JE, Hong KH, Park S, Preciado GT; Curr Genet. 1993;23:9-14. PMID:8381337