title: The elongation factor 3 unique in higher fungi and essential for protein biosynthesis is an E site factor.
abstract: Two elongation factors drive the ribosomal elongation cycle; elongation factor 1 alpha (EF-1 alpha) mediates the binding of an aminoacyl-tRNA to the ribosomal A site, whereas elongation factor 2 (EF-2) catalyzes the translocation reaction. Ribosomes from yeast and other higher fungi require a third elongation factor (EF-3) which is essential for the elongation process, but the step affected by EF-3 has not yet been identified. Here we demonstrate that the first and the third tRNA binding site (A and E sites, respectively) of yeast ribosomes are reciprocally linked; if the A site is occupied the E site has lost its binding capability, and vice versa, if the E site is occupied the A site has a low affinity for tRNAs. EF-3 is essential for EF-1 alpha-dependent A site binding of amino-acyl-tRNA only when the E site is occupied with a deacylated tRNA. The ATP-dependent activity of EF-3 is required for the release of deacylated tRNA from the E site during A site occupation.
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, AG Ribosomen, Berlin, Germany.
authors.forename: F J
authors.initials: FJ
authors.lastname: Triana-Alonso
authors.forename: K
authors.initials: K
authors.lastname: Chakraburtty
authors.forename: K H
authors.initials: KH
authors.lastname: Nierhaus
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D005656:Fungal Proteins; D005658:Fungi / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D020648:Peptide Elongation Factor 1; D020652:Peptide Elongation Factor 2; D010445:Peptide Elongation Factors / Q000378:metabolism*; D014176:Protein Biosynthesis; D012331:RNA, Fungal / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis / Q000378:metabolism*; D012343:RNA, Transfer / Q000378:metabolism*; D012360:RNA, Transfer, Phe / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D013997:Time Factors
chemical_list: D005656:Fungal Proteins; D020648:Peptide Elongation Factor 1; D020652:Peptide Elongation Factor 2; D010445:Peptide Elongation Factors; D012331:RNA, Fungal; D012333:RNA, Messenger; D012360:RNA, Transfer, Phe; D029701:Saccharomyces cerevisiae Proteins; C111584:YEF3 protein, S cerevisiae; D000255:Adenosine Triphosphate; D012343:RNA, Transfer