THE RIBOSOME-IN-PIECES - BINDING OF ELONGATION-FACTOR EF-G TO OLIGORIBONUCLEOTIDES THAT MIMIC THE SARCIN RICIN AND THIOSTREPTON DOMAINS OF 23S RIBOSOMAL-RNA/

An oligoribonucleotide (a 27-mer) that mimics the sarcin/ricin (S/R) d omain of Escherichia coli 23S rRNA binds elongation factor EF-G; the K -d is 6.9 mu M, whereas for binding to ribosomes it is 0.7 mu M. Bindi ng saturates when EF-G and the S/R RNA are equimolar; at saturation 70 % of the input RNA is in complexes with EF-G. Binding of EF-G to S/R R NA does not require GTP but is inhibited by GDP; the inhibition by GDP is overcome by GTP, The effects of mutations of the S/R domain nucleo tides G2655, A2660, and G2661 suggest that EF-G recognizes the conform ation of the RNA rather than the identity of the nucleotides. EF-G als o binds to an oligoribonucleotide (an 84-mer) that has the thiostrepto n region of 23S rRNA; however, EF-G binds independently to S/R and thi ostrepton oligoribonucleotides.