Isolation and study of some properties of the highly active 30S and 50S Escherichia coli ribosomal subunits.

A method for the isolation of highly active Escherichia coli ribosomal subunits has been described and used to obtain 30S subunits, which are fully active in the cistron-specific binding of tRNA, and reassociated 70S ribosomes, which are at least 35% active in the synthesis of polypeptides. The dissociation constants (Kd) of the 30S-poly(U)-tRNAPhe complex, which proved to be practically identical for tRNAPhe in the deacylated and aminoacylated forms, as well as for the chemically synthesized peptidyl-tRNA, have been measured. Changes in the binding conditions (temperatures from 0 to 30 degrees, Mg2+ concentrations from 20 to 5 mM, and NH4+ concentrations from 200 to 50mM) have a significant effect on the value of Kd without altering the number of active 30S subunits. It has been shown that the codon-specific binding of tRNA to the 30S subunits is completely reversible. The 30S subunits are not only not inactivated after a single act of binding of a tRNA molecule, but are capable of undergoing this process repeatedly without any appreciable loss in activity.