Mapping the fMet-tRNA(f)(Met) binding site of initiation factor IF2

The interaction between fMet-tRNA(f)(Met) and Bacillus stearothermophilus t ranslation initiation factor IF2 has been characterized. We demonstrate tha t essentially all thermodynamic determinants governing the stability and th e specificity of this interaction are localized within the acceptor hexanuc leotide fMet-3'ACCAAC of the initiator tRNA and a fairly small area at the surface of the beta-barrel structure of the 90-amino acid C-terminal domain of IF2 (IF2 C-2), A weak but specific interaction between IF2 C-2 and form yl-methionyl was also demonstrated. The surface of IF2 C-2 interacting with fMet.tRNA(f)(Met) has been mapped using two independent approaches, site-d irected mutagenesis and NMR spectroscopy, which yielded consistent results. The binding site comprises C668 and G715 located in a groove accommodating the methionyl side-chain, R700, in the vicinity of the formyl group, Y701 and K702 close to the acyl bond between fMet and tRNA(f)(Met), and the surf ace lined with residues K702-S660, along which the acceptor arm of the init iator tRNA spans in the direction 3' to 5'.