title: Role of guanine nucleotides in protein synthesis. Elongation factor G and guanosine 5'-triphosphate,3'-diphosphate.
abstract: The possible role of guanosine 5'-triphosphate,3'-diphosphate (pppGpp) in protein synthesis by Escherichia coli ribosomes and protein factors was examined. Although pppGpp could effectively substitute for GTP in reactions catalyzed by initiation factor 2 (ribosomal binding of fMet-tRNA and formation of N-formylmethionylpuromycin) and elongation factor T (ribosomal binding of Phe-tRNA and formation of dipeptidyl-tRNA), pppGpp poorly supported polyphenylalanine synthesis. The interaction of elongation factor G with pppGpp was, therefore, examined in detail. The nucleotide was found to be almost without activity in the translocation reaction, as measured by formation of N-acetylphenylalanyl-phenylalanylpuromycin. Nevertheless, the rate of the catalytic hydrolysis of pppGpp to guanosine 5'-diphosphate,3'-diphosphate by elongation factor G and ribosomes was about 30% of the rate of hydrolysis of GTP, a rate of hydrolysis that significantly exceeded the rate of translocation with GTP. Moreover, the rates of the fusidic acid-dependent, elongation factor G-dependent binding of pppGpp and ppGpp to ribosomes were about 75 to 85% the rates of GTP and GDP binding, respectively. We also found that dGTP could substitute for GTP in all reactions examined.
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis*; D004926:Escherichia coli / Q000378:metabolism; D006150:Guanine Nucleotides / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006868:Hydrolysis; D010452:Peptide Biosynthesis; D010442:Peptide Chain Initiation, Translational; D010445:Peptide Elongation Factors; D010649:Phenylalanine / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D012343:RNA, Transfer / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D006150:Guanine Nucleotides; D010445:Peptide Elongation Factors; D010761:Phosphorus Radioisotopes; D010649:Phenylalanine; D006160:Guanosine Triphosphate; D012343:RNA, Transfer