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A protein factor enhancing activation of inactive 30-S ribosomal subunits of Escherichia coli.

A protein factor partially purified from the S-100 fraction (supernatant from 100 000 x g spin) of Escherichia coli stimulates the conversion of 30-S ribosomal subunits from an inactive to an active form. The subunits are normally inactivated at low concentrations of Mg2+ and reactivated when heated under appropriate ionic conditions. The factor, which differs from the known soluble factors required for protein biosynthesis as well as from proteins of the 30-S subunit, enhances activation under conditions which by themselves allow for only a low level of activity to reappear. Fully active ribosomes and the assay reactions are not affected by the factor, indicating that its effect must be restricted to the activation process. The factor is likely to function by facilitating a conformational transition in the ribosome, and might act in vivo in a similar manner.