title: An essential component of a novel bacterial protein export system with homologues in plastids and mitochondria.
abstract: Proteins are transported across the bacterial plasma membrane and the chloroplast thylakoid membrane by means of protein translocases that recognize N-terminal targeting signals in their cognate substrates. Transport of many of these proteins involves the well defined Sec apparatus that operates in both membranes. We describe here the identification of a novel component of a bacterial Sec-independent translocase. The system probably functions in a similar manner to a Sec-independent translocase in the thylakoid membrane, and substrates for both systems bear a characteristic twin-arginine motif in the targeting peptide. The translocase component is encoded in Escherichia coli by an unassigned reading frame, yigU, disruption of which blocks the export of at least five twin-Arg-containing precursor proteins that are predicted to bind redox cofactors, and hence fold, prior to translocation. The Sec pathway remains unaffected in the deletion strain. The gene has been designated tatC (for twin-arginine translocation), and we show that homologous genes are present in a range of bacteria, plastids, and mitochondria. These findings suggest a central role for TatC-type proteins in the translocation of tightly folded proteins across a spectrum of biological membranes.
authors.affiliation: Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, United Kingdom.
authors.forename: E G
authors.initials: EG
authors.lastname: Bogsch
authors.forename: F
authors.initials: F
authors.lastname: Sargent
authors.forename: N R
authors.initials: NR
authors.lastname: Stanley
authors.forename: B C
authors.initials: BC
authors.lastname: Berks
authors.forename: C
authors.initials: C
authors.lastname: Robinson
authors.forename: T
authors.initials: T
authors.lastname: Palmer
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D005560:Formate Dehydrogenases / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D016366:Open Reading Frames; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism; D010940:Plant Proteins; D018087:Plastids / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C109236:Hcf106 protein, plant; D008565:Membrane Proteins; D010940:Plant Proteins; D021382:Protein Sorting Signals; D005560:Formate Dehydrogenases; D010089:Oxidoreductases, N-Demethylating; C023186:trimethylamine dehydrogenase