title: Identification of a novel translation factor necessary for the incorporation of selenocysteine into protein.
abstract: During the biosynthesis of selenoproteins in both prokaryotes and eukaryotes, selenocysteine is cotranslationally incorporated into the nascent polypeptide chain through a process directed by a UGA codon that normally functions as a stop codon. Recently, four genes have been identified whose products are required for selenocysteine incorporation in Escherichia coli. One of these genes, selC, codes for a novel transfer RNA species (tRNAUCA) that accepts serine and cotranslationally inserts selenocysteine by recognizing the specific UGA codon. The serine residue attached to this tRNA is converted to selenocysteine in a reaction dependent on functional selA and selD gene products. By contrast, the selB gene product (SELB) is not required until after selenocysteyl-tRNA biosynthesis. Here we present evidence indicating that SELB is a novel translation factor. The deduced amino-acid sequence of SELB exhibits extensive homology with the sequences of the translation initiation factor-2 (IF-2) and elongation factor Tu (EF-Tu). Furthermore, purified SELB protein binds guanine nucleotides in a 1:1 molar ratio and specifically complexes selenocysteyl-tRNAUCA, but does not interact with seryl-tRNAUCA. Thus, SELB could be an amino acid-specific elongation factor, replacing EF-Tu in a special translational step.
authors.affiliation: Lehrstuhl für Mikrobiologie der Universität, München, FRG.
authors.forename: K
authors.initials: K
authors.lastname: Forchhammer
authors.forename: W
authors.initials: W
authors.lastname: Leinfelder
authors.forename: A
authors.initials: A
authors.lastname: Böck
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D003545:Cysteine / Q000378:metabolism; D005798:Genes, Bacterial; D007700:Kinetics; D008969:Molecular Sequence Data; D011485:Protein Binding; D014176:Protein Biosynthesis; D011506:Proteins; D012345:RNA, Transfer, Amino Acid-Specific / Q000378:metabolism; D012643:Selenium / Q000378:metabolism*; D017279:Selenocysteine; D051140:Selenoproteins; D012689:Sequence Homology, Nucleic Acid
chemical_list: D001426:Bacterial Proteins; D011506:Proteins; D012345:RNA, Transfer, Amino Acid-Specific; C061878:SelB protein, Bacteria; D051140:Selenoproteins; C036928:tRNA, selenocysteine-; D017279:Selenocysteine; D012643:Selenium; D003545:Cysteine