Fluoroaluminates are thought to mimic the γ-phosphate of GTP and thus, together with GDP, perturb the functioning of heterotrimeric GTP-binding G-proteins. Here we show they do inhibit the ribosome-stimulated GTPase activity of EF-G from Escherichia coli via the formation of a stable complex with EF-G·GDP and ribosomes. In contrast, no perturbed interactions were observed in a similar ribosomal complex with EF-Tu. Interestingly, in the absence of ribosomes both EF-Tu and EF-G remain totally unaffected by fluoroaluminates. For members of the GTPase superfamily such differential effects have not been described before.
