title: Properties of tRNA species modified in the 3'-terminal ribose moiety in an eukaryotic ribosomal system.
abstract: Phe-tRNAPhe species modified on the 3'-terminal ribose residue were investigated for their ability to participate in individual steps of the elongation cycle using eukaryotic ribosomes from reticulocytes. None of the Phe-tRNAs used, namely Phe-tRNAPhe-C-C-3'dA, Phe-tRNAPhe-C-C-3'-NH2A, and Phe-tRNAPhe-C-C-Aoxi-red, can function in the overall process. All modified Phe-tRNAPhe species can be bound nonenzymatically to ribosomes. Phe-tRNAPhe-C-C-3'NH2A exhibits exceptionally high binding at low Mg2+ concentration compared with Phe-tRNAPhe-C-C-A binding. Ac-Phe-tRNAPhe species prepared from the three modified tRNAs, when bound to the donor site, were devoid of donor activity. The enzymatic binding of both Phe-tRNAPhe-C-C-3'dA and Phe-tRNAPhe-C-C-3'NH2A is less efficient than that of Phe-tRNAPhe-C-C-A but these Phe-tRNAPhe species have acceptor activity. Phe-tRNAPhe-C-C--Aoxi-red is not a substrate for the EF-I promoted binding reaction and has no acceptor activity. The nonaminoacylated species, tRNAPhe-C-C-A, tRNAPhe-C-C-3'dA, and tRNAPhe-C-C-3'NH2A, bind to the ribosome to a larger extent than the corresponding aminoacylated tRNAs, both in the presence and in the absence of poly(U). Peptidyl-tRNAPhe-C-C-3'dA bound to the donor site cannot activate the acceptor site for EF-I promoted binding of Phe-tRNAPhe as does peptidyl-tRNAPhe-C-C-A. Further, it was observed that a correct codon-anticodon interaction influences the recognition of the 3' terminus of tRNA. Specificity of eukaryotic ribosomes for the 2'- and/or 3'-aminoacylated tRNA species is discussed and compared with the properties of Escherichia coli system.
mesh_terms: D001665:Binding Sites; D007700:Kinetics; D010441:Peptide Chain Elongation, Translational; D010445:Peptide Elongation Factors; D010649:Phenylalanine; D010652:Phenylalanine-tRNA Ligase / Q000378:metabolism; D011072:Poly U / Q000378:metabolism; D012343:RNA, Transfer / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D013329:Structure-Activity Relationship; D014158:Transcription, Genetic
chemical_list: D010445:Peptide Elongation Factors; D011072:Poly U; D010649:Phenylalanine; D012343:RNA, Transfer; D010652:Phenylalanine-tRNA Ligase