Reconstitution of biologically active 50S ribosomal subunits with artificial 5S RNA molecules carrying disturbances in the base pairing within the molecular stalk.

Bacillus stearothermophilus 50S ribosomal subunits were reconstituted in vitro using artificial 5S RNA molecules constructed by combining parts of major and minor type (Raué et al. (1976) Europ. J. Biochem. 68, 169-176) B. licheniformis 5S RNA. The artificial 5S RNA molecules carry defined disturbances (A.C juxtapositions and extra G.U pairs) in the base pairing between the 5'- and 3'-terminal sequences of the molecule (the molecular stalk region). The biological activity of the reconstituted subunits was determined in an E. coli cell-free system programmed with poly-U. The results show that conservation of the base pairing within the molecular stalk is not required for biological activity of 5S RNA. Disturbances of the base pairing within this region do reduce the rate of reconstitution, however. Normal base pairing in the molecular stalk is thus required to ensure efficient ribosome assembly.