Interaction between initiator Met-tRNAfMet and elongation factor EF-Tu from E. coli.

It has recently been shown that the non-formylated initiator Met-tRNAfMet from E. coli can form a stable ternary complex with the elongation factor EF-Tu and GTP. Using the protection of EF-Tu:GTP against spontaneous hydrolysis of the aminoacylester bond of Met-tRNAfMet, we confirm these results, and show that the protection is specific for the non-formylated form of the initiator tRNA. The ternary complex Met-tRNAfMet:EF-Tu:GTP can be isolated by column chromatography in a way similar to that demonstrated previously with EF-Tu complexed to the elongator Met-tRNAmMet. 32P-labeled Met-tRNAfMet within the ternary complex was analyzed by the footprinting technique. The pattern of initiator tRNA protection by EF-Tu against ribonuclease digestion is not significantly different from the one found previously for elongator tRNAs. These results lead us to suggest that the initiator tRNAfMet, under growth conditions which do not permit formylation, may to some extent function as an elongator tRNA.