Methionyl-tRNAs and initiation of protein synthesis in vicia faba (L.)

Nucleotide sequence of wheat germ cytoplasmic initiator methionine transfer ribonucleic acid

The primary sequence of wheat germ initiator tRNA has been determined using in vitro labelling techniques. The sequence is: pAUCAGAGUm1Gm2GCGCAG CGGAAGCGUm2GG psi GGGCCCAUt6AACCCACAGm7GDm5Cm5CCAGGA psi CGm1AAACCUG*GCUCUGAUACCAOH. As in other eukaryotic initiator tRNAs, the sequence -T psi CG(A)- present in loop IV of virtually all tRNA active in protein synthesis is absent and is replaced by -A psi CG-. The base pair G2:C71 present in all other initiator tRNAs recognized by E. coli Met-tRNA transformylase is absent and is replaced by U2:A71. Since wheat germ initiator tRNA is not formylated by E. coli Met-tRNA transformylase this implies a possible role of the G2:C71 base pair present in other initiator tRNAs in formylation of initiator tRNA species.

Aminoacylation of Phaseolus vulgaris cytoplasmic, chloroplastic and mitochondrial tRNAsMet and of Escherichia coli tRNAsMet by homologous and heterologous enzymes

Met-tRNA synthetase from Paseolus vulgaris cytoplasm could be separated from its chloroplastic or mitochondrial counterpart by DEAE-cellulose chromatography, but the Met-tRNA synthetase from the two latter organelles could not be distinguished using DEAE-cellulose, hydroxyapatite or CM-Sephadex chromatography. As revealed by reverse-phase chromatography, bean cytoplasm contains 2 tRNAsMet; only one is charged by chloroplast, mitochondrial or Escherichia coli Met-tRNA synthetase. Mitochondria contain, in addition to the 2 cytoplasmic tRNAsMet, 3 mitochondria-spedific tRNAsMet; 2 can be formylated by the mitochondrial or the E. coli transformylase; all 3 are charged by mitochondrial, chloroplastic or E, coli Met-tRNA synthetase; none is charged by the cytoplasmic enzyme. Chloroplasts contain, in addition to the 2 cytoplasmic tRNAsMet, 3 chloroplast-specific tRNAsMet, different from the mitochondrial tRNAsMet; one is formylatable by the chloroplastic or the E. coli transformylase; all 3 are charged by chloroplastic, mitochondrial or E. coli Met-tRNA synthetase; only one is charged by the cytoplasmic enzyme. Of the 3 E. coli tRNAsMet, only the formylatable species can be charged by bean cytoplasmic, chloroplastic or mitochondrial Met-tRNA synthetase.