TOPOGRAPHY OF THE ESCHERICHIA-COLI INITIATION-FACTOR-2 FMET-TRNA(F)(MET) COMPLEX AS STUDIED BY CROSS-LINKING

trans-Diamminedichloroplatinum(II) was used to induce reversible cross -links between Escherichia coli initiation factor 2 (IF-2) and fMet-tR NA(f)(Met). Two distinct cross-links between IF-2 and the initiator tR NA were produced. Analysis of the cross-linking legions on both RNA an d protein moieties reveals that the T arm of the tRNA is in the proxim ity of a region of the C-terminal domain of IF-2 (residues Asn(611)-Ar g(645)) This cross-link is well-correlated with the fact that the C-do main of IF-2 contains the fMet-tRNA binding site and that the cross-li nked RNA fragment precisely maps in a region which is protected by IF- 2 from chemical modification and enzymatic digestion, Rather unexpecte dly, a second cross-link was characterized which involves the anticodo n arm of fMet-tRNA(f)(Met) and the N-terminal part of IF-2 (residues T rp(215)-Arg(237)).