[Studies on the mechanism of translocation in ribosomes. IV. The role of ribisomal proteins S12 in translocation].

It is shown that ribosomes, the 30S subparticles of which are reconstituted without protein S12, read out poly(U) and synthesize polyphenylalanine in the absence of protein elongation factors (EF-T and EF-G) and GTP, i.e. perform "non-enzymatic" translation. On the contrary, ribosomes, the 30S subparticles of which are reconstituted with protein S12, do not display "non-enzymatic" translation without its activation with parachloromercuribenzoate. This means that a complete removal of protein S12 from the ribosome, as well as its damage with para-chloromercuribenzoate, leads to the unblocking of the potential ability of ribosomes for spontaneous ("non-enzymatic") translocation. The presence of intact protein S12 in the ribosome prevents spontaneous (EF-G-GTP-independent) translocation. A suggestion is made that the intact protein S12 forms an additional contact between the ribosomal subparticles and thus participates in the ribosomal mechanism of translocation by affecting the locking-unlocking of the subparticles.