RELATIONSHIP BETWEEN THE STRUCTURE AND FUNCTION OF ESCHERICHIA-COLI INITIATOR TRANSFER-RNA

Through functional studies of mutant tRNAs, we have identified sequenc e and/or structural features important for specifying the many distinc tive properties of E coli initiator tRNA. Many of the mutant tRNAs con tain an anticodon sequence change from CAU-->CUA and are now substrate s for E coli glutaminyl-tRNA synthetase (G1nRS). We describe here the effect of further mutating the discriminator base 73 and nucleotide 72 at the end of the acceptor stem on: i) recognition of the mutant tRNA s by E coli G1nRS; ii) recognition by E coil methionyl-tRNA transformy lase; and iii) activity of the mutant tRNAs in initiation in E coli. F or G1nRS recognition our results are, in general, consistent with inte ractions found in the crystal structure of the E coli G1nRS-glutamine tRNA complex. The results also support our previous conclusion that fo rmylation of initiator tRNA is important for its function in initiatio n.