Transfer ribonucleic acid deprived of the C-C-A 3'-extremity can interact with elongation factor Tu

In this work we describe that uncharged tRNAs or modified tRNAs lacking all or part of the C-C-A end (i.e., tRNA minus pCpCpA, tRNA minus pA, and tRNA minus A) can still influence the GTPase activity of the elongation factor Tu (EF-Tu), thus showing that, besides the aminoacylated 3'-end, other regions of the aa-tRNA interact with EF-Tu. The existence of an interaction between EF-Tu and truncated tRNAs was also confirmed by examining the dissociation of the EF-Tu-GTP complex: the rate of this reaction is decreased upon addition of tRNAVal1 minus pCpCpA. The effect on the EF-Tu GTPase activity of tRNAs deprived of the C-C-A 3'-end is still evident in the presence of C-C-A-aa. The stimulatory pattern obtained with C-C-A-Val at 5 mM MgCl2 is decreased upon addition of tRNAVal1 minus pCpCpA, tRNAVal1 minus pA, or tRNAVal1 minus A. This shows that the effect of the aminoacylated C-C-A 3'-end can be influenced via EF-Tu by the remaining regions of the tRNA, after cleavage of a bond in the 3'-extremity. However, also with an excess of tRNAVal1 minus pCpCpA over C-C-A-Val, no "aa-tRNA-like" effect, i.e., no inhibition of the EF-Tu GTPase, was obtained, suggesting that, upon binding with EF-Tu, a specific conformational change in the aa-tRNA molecule also takes place, regulating the expression of the GTPase activity. Our results unequivocally show that different regions of the aa-tRNA are needed for a coordinated interaction with EF-Tu.