Reconstitution of 48 S particles with subunit association activity from Escherichia coli 50 S ribosomal components.

Previous studies have shown that 50 S ribosomal proteins bind sequentially to RNA's of the 50 S subunit via temperature-dependent steps (0 leads to 37 leads to 55 degrees C) to form 28, 32, (43) and 48 S particles (Chu, F.K., and Maeba, P.Y. (1973) Can. J. Biochem. 51, 129-139). When three equivalents of 50 S ribosomal proteins are used per equivalent of 23 S RNA, the yield of reconstituted 48 S particles is greatly increased. The addition of 10 mM spermidine increases the rate of reconstitution and abolishes the need for prior incubation at lower temperatures when 48 S particles are formed at 55 degrees C. In the presence of excess 50 S ribosomal proteins and 10 mM spermidine, 48 S particles formed at 50 degrees C are able to associate with 30 S subunits in a stoichiometric manner to form 70 S complexes. These 48 S particles compete effectively with 50 S subunits for 30 S subunits and have an association activity equal to that of 50 S subunits. As compared to the 34 proteins in 50 S subunits, 4 are either absent or present in marginal amounts, 11 in reduced amounts, and 19 in approximately normal amounts in the 48 S particles.