The Involvement of Protein L 11 in the Joining of the 30‐S Initiation Complex to the 50‐S Subunit

Abstract

Ribosomal protein L11 participates in the coupling of the 30S initiation complex with the 50S subunit [Escherichia coli]. 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 30S initiation complex and 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 1 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 50S particles carrying thiostrepton, which prevents the binding of initiation factor IF-2 into the 70S initiation complex. L11 may induce a niche on the ribosomal surface to facilitate the proper binding of the IF-2.cntdot. GTP .cntdot. fMet-tRNA complex. This binding of IF-2 enables the 30S initiation complex to join to the 50S subunit, because of the associative ability of IF-2. If joining is impaired, the levels of fMet-tRNA binding and of the If-2-mediated GTP hydrolysis are lowered.