THE ROLE OF MODIFIED PURINE-64 IN INITIATOR ELONGATOR DISCRIMINATION OF TRANSFER RNAMET(I) FROM YEAST AND WHEAT-GERM

The role of 2′-ribosylated adenosine 64 in tRNAiMet from yeast in initiation/elongation discrimination was investigated. As measured by in vitro translation in rabbit reticulocyte lysate, the specific removal of the 2′-ribosylphosphate at adenosine 64 via periodate oxidation allows tRNAiMet to read internal AUG codons of the globine messenger RNA. Yeast Met-tRNAiMet lacking the modification of nucleoside 64 forms ternary complexes with GTP and elongation factor Tu from Escherichia coli. The lack of modification at position 64 does not prevent tRNAiMet from participating in the initiation process of in vitro protein synthesis. Wheat germ tRNAiMet has a 2′-ribosylated guanosine at position 64. Removal of this modification from the wheat germ tRNAiMet enables it to read internal AUG codons of globine and tobacco mosaic virus messenger RNA in reticulocyte and wheat germ translation systems, respectively. © 1990 Oxford University Press.