Our results suggest that the riboso

Our results suggest that the ribosome plays a previously unidentified dual role of both guanine-nucleotide exchange factor and GTPase-activating protein for at least two transla- tion factors in eubacteria, EF-G and RF3. This may be ration- alized by the requirement that ribosomal GTPase activity be strictly controlled [8] and that each of the translation factors must selectively target a particular state of the ribosome.