Stimulation of in vitro colicin E3 action by messenger ribonucleic acid and message analogs.

Ribosomes that are synthesizing polypeptides in vitro on certain natural and synthetic messages are more susceptible to inactivation by colicin E3 than ribosomes treated with E3 in the absence of added message. The initiation step of protein synthesis appears to be sufficient to cause the conversion of ribosomes to a state more sensitive to colicin E3. Message and protein synthesis are not, however, absolute requirements for the in vitro inactivation of ribosomes by colicin E3. The in vitro inactivation of ribosomes by E3 has a sharp magnesium optimum which correlates well with the magnesium optimum for in vitro protein synthesis. We conclude from these experiments that ribosomes in a state most competent for protein synthesis are most susceptible to inactivation by colicin E3.