A, incorporation of radio-labeled GTP. Binding reactions were assembled using [α-32P]GTP as a tracer and either no protein (mock), MoaB protein alone (MoaB), or MoaB protein with the listed divalent cations (+Mg/Ca/Mn). Protein precipitations were performed as described under “Experimental Procedures.” The amount of bound [α-32P]GTP was determined by scintillation counting and is expressed as a percentage of the total input [α-32P]GTP. B, GTPase activity. Binding reactions were assembled as in A. Protein was precipitated, acid-hydrolyzed, and analyzed by thin-layer chromatography as described under “Experimental Procedures.” Input [α-32P]GTP (lane 1) and enzymatically derived [α-32P]GDP (lane 2) were used as running standards.