Effects of macromolecular crowding on the association of E. coli ribosomal particles

The equilibrium for the binding reaction between the 30 S and 50 S ribosomal subunits of E. coli is shifted towards formation of 70 S ribosomes in the presence of a variety of polymers. The polymers also increase a further interaction between 70 S particles to form the 100 S dimer. The requirement for relatively high concentrations of non-specific polymers indicates that the shifts in equilibria arise from excluded volume effects. Analysis using scaled particle theory is consistent with this mechanism. The effects of high concentrations of polymers on the interactions between ribosomal species may make important changes in the function of ribosomes under the crowded conditions which occur in vivo.