Abstract
According to their role in translation, tRNAs specifically interact either with elongation factor Tu (EFTu) or with initiation factor 2 (IF2). We here describe the effects of overproducing EFTu and IF2 on the elongator versus initiator activities of various mutant tRNAMet species in vivo. The data obtained indicate that the selection of a tRNA through one or the other pathway of translation depends on the relative amounts of the translational factors. A moderate overexpression of EFTu is enough to lead to a misappropriation of initiator tRNA in the elongation process, whereas overproduced IF2 allows the initiation of translation to occur with unformylated tRNA species. In addition, we report that a strain devoid of formylase activity can be cured by the overproduction of tRNAMetf. The present study brings additional evidence for the importance of formylation in defining tRNAMetf initiator identity, as well as a possible explanation for the residual growth of bacterial strains lacking a functional formylase gene such as observed in Guillon, J. M., Mechulam, Y., Schmitter, J.-M., Blanquet, S., and Fayat, G. (1992) J. Bacteriol. 174, 4294-4301.
Highlights
Caryotes [13], governs both the recognition of the aminoacyltRNA by methionyl-ARNtfMet formyltransferase and its low affinity for the elongation factor elongation factor Tu (EFTu) [8, 14, 15]
Initiation of translation involves a specialized tRNAMet species that bears identity determinants that allow it to interact with the components of the initiation apparatus and prevent it to play with the elongation factors
The nucleotides of E. coli initiator tRNA determining its function have been studied by identity switching experiments; N-Acylation of the aminoacylated tRNA is required to observe the formation of a binary complex with initiation factor 2 (IF2) (20 –22)
Summary
Caryotes [13], governs both the recognition of the aminoacyltRNA by methionyl-ARNtfMet formyltransferase and its low affinity for the elongation factor EFTu [8, 14, 15]. The lack of a base pairing at positions 1–72 does not appear sufficient per se to prevent the initiator tRNA from entering the elongation pathway. A tRNAfMet with only the amber anticodon can become active in elongation provided that cells are rendered partially deficient in formyltransferase activity [6]. This latter result has led us to consider that formylation of methionyl-tRNAfMet could be important in preventing its misappropriation by the elongation apparatus. Initiation of translation involves a specialized tRNAMet species that bears identity determinants that allow it to interact with the components of the initiation apparatus and prevent it to play with the elongation factors.
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