Comparison of active and inactive forms of the E. coli 30S ribosomal subunits

Dissociation of E. Coli 70S ribosomes in the presence of 0.1 mM Mg++ yields partially inactivated 30S and 50S subunits. This inactivation can be avoided by dissociating the 70S ribosome in a medium containing 10 mM Mg++. 400 mM Na+. Comparison of the active and inactive forms of the 30S and 50S subunits has led to the following conclusions: 1) The two forms possess identical (50S subunits) or very similar (30S subunits) hydrodynamic properties. No differences in their morphologies is detectable by electron microscopy. 2) They possess the same protein compositions except for the presence of a larger amount of protein S1 in the inactive than in the active form of the 30S subunit. 3) They differ significantly in functional properties: more efficient association of the active than of the inactive forms with the complementary subunit; extensive dimerization of inactive 30S subunits in the presence of 10 mM Mg++; no dimerization of active 30S subunits under the same conditions; six-fold higher peptidyl transferase activity of active as compared to inactive 50S subunits.