Proteolysis of Bacillus stearothermophilus IF2 and specific protection by fMet-tRNA

Abstract

Translation initiation factor IF2 from Bacillus steaiothermophilus (741 amino acids, M r 82,043) was subjected to trypsinolysis alone or in the presence of fMet-tRNA. The initiator tRNA was found to protect very efficiently the Arg 308-Ala 309 bond within the GTP binding site of IF2 and, more weakly, three bonds (Lys 146-Gln 147, Lys 154-Glu 155 and Arg 519-Ser 520). The first two are located at the border between the non-conserved, dispensable (for translation) N-terminal portion and the conserved G-domain of the protein, the third is located at the border between the G- and C-domains. Since IF2 is known to interact with fMet-tRNA through its protease-resistant C- (carboxyl terminus) domain, the observed protection suggests that, upon binding or fMet-tRNA, long-distance tertiary interactions between the IF2 domains may take place.