title: Sequence and phylogenetic analyses of the twin-arginine targeting (Tat) protein export system.
abstract: Twin-arginine targeting (Tat) protein secretion systems consist of two protein types, members of the TatA and TatC families. Homologues of these proteins are found in many archaea, bacteria, chloroplasts and mitochondria. Every prokaryotic organism with a fully sequenced genome exhibits either neither family member, or between one and three paralogues of these two family members. The Arabidopsis thaliana genome encodes three of each. Although many mitochondrially encoded TatC homologues have been identified, corresponding TatA homologues have not been found in this organelle. Phylogenetic analyses reveal that most prokaryotic Tat systems consist of one TatC homologue and two sequence-divergent TatA homologues (TatA and TatB). When only one TatA homologue is present, TatB is missing, and when three TatA homologues are present, the third one arose by duplication of TatA, not TatB. Further, homologues most resembling TatB are more sequence-divergent than those more closely resembling TatA. In contrast to the TatA family, the TatC family shows phylogenetic clustering in strict accordance with organismal type. These results are discussed in terms of their probable structural, functional and evolutionary significance.
authors.affiliation: Department of Biology, University of California at San Diego, La Jolla 92093-0116, USA.
authors.forename: Ming-Ren
authors.initials: MR
authors.lastname: Yen
authors.forename: Yi-Hsiung
authors.initials: YH
authors.lastname: Tseng
authors.forename: Erin H
authors.initials: EH
authors.lastname: Nguyen
authors.forename: Long-Fe
authors.initials: LF
authors.lastname: Wu
authors.forename: Milton H
authors.initials: MH
authors.lastname: Saier
mesh_terms: D001120:Arginine / Q000737:chemistry; D001426:Bacterial Proteins / Q000235:genetics; D005075:Biological Evolution; D001692:Biological Transport; D029968:Escherichia coli Proteins / Q000235:genetics*; D026901:Membrane Transport Proteins / Q000235:genetics*; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D020033:Protein Isoforms / Q000235:genetics; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D020033:Protein Isoforms; C499697:TatA protein, E coli; C461379:TatC protein, E coli; C408585:twin-arginine translocase complex, E coli; D001120:Arginine