title: A homologue of a nuclear-coded iron-sulfur protein subunit of bovine mitochondrial complex I is encoded in chloroplast genomes.
abstract: The chloroplast genomes of Marchantia polymorpha, Nicotiana tabacum, and Oryza sativa contain open reading frames (ORFs or potential genes) encoding homologues of some of the subunits of mitochondrial NADH:ubiquinone oxidoreductase (complex I). Seven of these subunits (ND1-ND4, ND4L, ND5, and ND6) are products of the mitochondrial genome, and two others (the 49- and 30-kDa components of the iron-sulfur protein fraction) are nuclear gene products. These findings have been taken to indicate the presence in chloroplasts of an enzyme related to complex I, possibly an NAD(P)H:plastoquinone oxidoreductase, participating in chlororespiration. This view is reinforced by the present work in which we have shown that chloroplast genomes encode a homologue of the 23-kDa subunit, another nuclear-encoded component of bovine complex I. The 23-kDa subunit is in the hydrophobic protein fraction of the enzyme, the residuum after removal of the flavoprotein and iron-sulfur protein fractions. The sequence motif CysXXCysXXCysXXXCysPro, which provides ligands for tetranuclear iron-sulfur centers in ferredoxins, occurs twice in its polypeptide chain and is evidence of two associated 4Fe-4S clusters. This is the only iron-sulfur protein identified so far in the hydrophobic protein fraction of complex I, and so it is possible that one of these centers is that known as N-2, the donor of electrons to ubiquinone. The sequence of the 23-kDa subunit is closely related to potential proteins, which also contain the cysteine-rich sequence motifs, encoded in the frxB ORFs in chloroplast genomes.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Medical Research Council Laboratory of Molecular Biology, Cambridge, U.K.
authors.forename: A
authors.initials: A
authors.lastname: Dupuis
authors.forename: J M
authors.initials: JM
authors.lastname: Skehel
authors.forename: J E
authors.initials: JE
authors.lastname: Walker
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002417:Cattle; D002736:Chloroplasts / Q000201:enzymology*; D003001:Cloning, Molecular; D017343:Genes, Plant; D007506:Iron-Sulfur Proteins / Q000235:genetics* / Q000302:isolation & purification; D046911:Macromolecular Substances; D008929:Mitochondria, Heart / Q000201:enzymology*; D008969:Molecular Sequence Data; D016660:NAD(P)H Dehydrogenase (Quinone); D016366:Open Reading Frames; D010944:Plants / Q000201:enzymology / Q000235:genetics*; D010947:Plants, Toxic; D011808:Quinone Reductases / Q000235:genetics* / Q000302:isolation & purification; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D014026:Nicotiana / Q000235:genetics
chemical_list: D007506:Iron-Sulfur Proteins; D046911:Macromolecular Substances; D016660:NAD(P)H Dehydrogenase (Quinone); D011808:Quinone Reductases