Translation initiation factor IF2 from Bacillus stearothermophilus (741 amino acids, M r = 82 043) was subjected to trypsinolysis alone or in the presence of GTP. Following electroblotting and automated amino acid sequencing of the resulting peptides, the location and the sequential order of the main cleavage sites were identified. Trypsinolysis of IF2 ultimately generates two compact domains: a 24.5 kDa C-terminal fragment and a 40 kDa G-fragment which is obtained only in the presence of GTP which strongly protects a cleavage site within the GTP binding domain.
