title: Primary structure and mitochondrial import in vitro of the 20.9 kDa subunit of complex I from Neurospora crassa.
abstract: The 20.9 kDa subunit of NADH:ubiquinone oxidoreductase (complex I) from Neurospora crassa is a nuclear-coded component of the hydrophobic arm of the enzyme. We have determined the primary structure of this subunit by sequencing a full-length cDNA and a cleavage product of the isolated polypeptide. The deduced protein sequence is 189 amino acid residues long and contains a putative membrane-spanning domain. Striking similarity over a 60 amino-acid-residue domain with the M (matrix) protein of para-influenza virus was found. No other relationship with already known sequences could be detected, leaving the function of this subunit in complex I still undefined. The biogenetic pathway of this polypeptide was studied using a mitochondrial import system in vitro. The 20.9 kDa subunit synthesized in vitro is efficiently imported into isolated mitochondria, where it obtains distinct features of the endogenous subunit. Our results suggest that the 20.9 kDa polypeptide is made on cytosolic ribosomes lacking a cleavable targeting sequence, interacts with the mitochondrial outer membrane (in a process that does not require an energized inner membrane), and is imported into mitochondria at contact sites. The 20.9 kDa subunit is then inserted into the inner membrane acquiring a topology similar to that of the already assembled subunit.
authors.affiliation: Institut für Physiologische Chemie, Universität München, Federal Republic of Germany.
authors.forename: J E
authors.initials: JE
authors.lastname: Azevedo
authors.forename: U
authors.initials: U
authors.lastname: Nehls
authors.forename: C
authors.initials: C
authors.lastname: Eckerskorn
authors.forename: H
authors.initials: H
authors.lastname: Heinrich
authors.forename: H
authors.initials: H
authors.lastname: Rothe
authors.forename: H
authors.initials: H
authors.lastname: Weiss
authors.forename: S
authors.initials: S
authors.lastname: Werner
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D015153:Blotting, Western; D003001:Cloning, Molecular; D003488:Cyanogen Bromide; D004247:DNA / Q000737:chemistry; D008564:Membrane Potentials; D008928:Mitochondria / Q000201:enzymology*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009492:Neurospora crassa / Q000201:enzymology* / Q000648:ultrastructure; D010446:Peptide Fragments / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D014763:Viral Matrix Proteins / Q000737:chemistry
chemical_list: C031540:M-protein, influenza virus; D010446:Peptide Fragments; D014763:Viral Matrix Proteins; D004247:DNA; D016660:NAD(P)H Dehydrogenase (Quinone); D003488:Cyanogen Bromide