title: Reduced turnover of the elongation factor EF-1 X ribosome complex after treatment with the protein synthesis inhibitor II from barley seeds.
abstract: The effect of the protein synthesis inhibitor II from barley seeds (Hordeum sp.) on protein synthesis was studied in rabbit reticulocyte lysates. Inhibitor treatment of the lysates resulted in a rapid decrease in amino acid incorporation and an accumulation of heavy polysomes, indicating an effect of the inhibitor on polypeptide chain elongation. The protein synthesis inhibition was due to a catalytic inactivation of the large ribosomal subunit with no effect on the small subparticle. The inhibitor-treated ribosomes were fully active in participating in the EF-1-dependent binding of [14C]phenylalanyl-tRNA to poly(U)-programmed ribosomes in the presence of GTP and the binding of radioactively labelled EF-2 in the presence of GuoPP[CH2]P. Furthermore, the ribosomes were still able to catalyse peptide-bond formation. However, the EF-1- and ribosome-dependent hydrolysis of GTP was reduced by more than 40% in the presence of inhibitor-treated ribosomes, while the EF-2- and ribosome-dependent GTPase remained unaffected. This suggests that the active domains involved in the two different GTPases are non-identical. Treatment of reticulocyte lysates with the barley inhibitor resulted in a marked shift of the steady-state distribution of the ribosomal phases during the elongation cycle as determined by the ribosomal content of elongation factors. Thus, the content of EF-1 increased from 0.38 mol/mol ribosome to 0.71 mol/mol ribosome, whereas the EF-2 content dropped from 0.20 mol/mol ribosome at steady state to 0.09 mol/mol ribosome after inhibitor treatment. The data suggest that the inhibitor reduces the turnover of ribosome-bound ternary EF-1 X GTP X aminoacyl-tRNA complexes during proof-reading and binding of the cognate aminoacyl-tRNA by inhibiting the EF-1-dependent GTPase.
mesh_terms: D000818:Animals; D020963:GTP Phosphohydrolase-Linked Elongation Factors / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D001467:Hordeum; D046911:Macromolecular Substances; D010441:Peptide Chain Elongation, Translational / Q000187:drug effects; D020648:Peptide Elongation Factor 1; D020652:Peptide Elongation Factor 2; D010445:Peptide Elongation Factors / Q000378:metabolism*; D010458:Peptidyl Transferases / Q000378:metabolism; D010936:Plant Extracts / Q000494:pharmacology*; D037121:Plant Lectins; D011817:Rabbits; D051381:Rats; D012156:Reticulocytes / Q000378:metabolism; D012270:Ribosomes / Q000187:drug effects* / Q000378:metabolism; D012276:Ricin / Q000494:pharmacology; D012639:Seeds
chemical_list: D046911:Macromolecular Substances; D020648:Peptide Elongation Factor 1; D020652:Peptide Elongation Factor 2; D010445:Peptide Elongation Factors; D010936:Plant Extracts; D037121:Plant Lectins; D006160:Guanosine Triphosphate; D012276:Ricin; D010458:Peptidyl Transferases; D020963:GTP Phosphohydrolase-Linked Elongation Factors