The involvement of protein L11 in the joining of the 30-S initiation complex to the 50-S subunit.

Ribosomal protein L11 participates in the coupling of the 30-S initiation complex with the 50-S subunit. P37 cores, lacking L7, L8, L12, L33, L10 and L11 were reconstituted with L7 and L10. These particles are unable to join successfully to the 30-S initiation complex, whereas reconstitution of the same cores in the presence of L7, L10 and L11 restores 60-80% of the original coupling activity. P0 cores lacking only L7, L8, L12 and L33 are able to carry out one round of initiation, addition of L7 resulting in complete restoration of full activity. The data obtained with these P37 core particles resemble those obtained with untreated 50-S particles carrying thiostrepton, which prevents the binding of initiation factor IF-2 into the 70-S initiation complex. It is postulated that L11 induces a niche on the ribosomal surface to facilitate the proper binding of the IF-2 X GTP X fMet-tRNA complex. This binding of IF-2 enables the 30-S initiation complex to join to the 50-S subunit, because of the associative ability of IF-2. If joining is impaired than both the level of fMet-tRNA binding and of the IF-2-mediated GTP hydrolysis is lowered.