Role of 5S RNA in the functions of 50S ribosomal subunits.

50S ribosomal subunits from Bacillus stearothermophilus can be reconstituted from their dissociated components, namely a 5S RNA-free protein fraction, a 5S RNA-free 23S ribosomal RNA fraction, and purified 5S RNA. The biological activity of reconstituted particles in polypeptide synthesis is dependent on the presence of 5S RNA. In the absence of 5S RNA, particles are produced that have greatly reduced activity in (a) polypeptide synthesis directed by synthetic, as well as natural, messenger RNA, (b) peptidyl transferase assay, (c) [(3)H]UAA binding dependent on peptide chain termination factor R1, (d) G factor-dependent [(3)H]GTP binding, and (e) codon-directed tRNA binding assayed in the presence of 30S subunits. Thus, 5S RNA is an essential 50S ribosomal component.