Binding of aminoacyl-tRNA to reconstituted subparticles of Escherichia coli large ribosomal subunits.

The activity of 50-S subunits to stimulate the binding of aminoacyl-tRNA to the 30-S subunits was lost when the particles were washed with LiCl concentrations higher than 1.0 M [Kazemie, M. (1975) Eur. J. Biochem. 58,501-510]. The particles could regain this activity when they were incubated with the corresponding LiCl washes. This effect of LiCl washes was used as an assay for identification of 50-S subunit proteins which are essential for binding of aminoacyl-tRNA. A protein mixture containing mainly Ll, Lll and L16 can reactivate 50-S "core" particles, consisting of 10 proteins and 23-S RNA, to bind aminoacyl-tRNAs in the presence of 30-S subunits. Besides 5-S RNA, protein L24 has a stimulatory effect on the binding of aminoacyl-tRNA. Proteins L2, L20 and L23 are possibly required for maintaining the 50-S subunits in the correct conformation for binding of aminoacyl-tRNAs.