FIGURE 1.

XLG2 has GTP binding activity in the presence of Ca²⁺. A, time course of [³⁵S]GTPγS binding to GPA1 and lack of [³⁵S]GTPγS binding to XLG2C in the presence of MgCl₂. 100 nm XLG2C was incubated at 30 °C with 0.2 μm [³⁵S]GTPγS in the presence of 10 mm MgCl₂. 100 nm His₆ TRX and 100 nm His₆ TRX-tagged GPA1 were used as negative and positive controls, respectively. Aliquots (20 μl) were withdrawn at the indicated time points, filtered, and subjected to scintillation counting. B, time course of [³⁵S]GTPγS binding to XLG2 in the presence of different concentrations of Ca²⁺. 100 nm XLG2C was incubated at 30 °C with 0.2 μm [³⁵S]GTPγS in the presence or absence of 10 mm CaCl₂. C, [³⁵S]GTPγS binding to XLG2C, its mutant form XLG2C(T475N), and GPA1 in the presence of CaCl₂ or MgCl₂. The amount of [³⁵S]GTPγS binding to XLG2C, XLG2C(T475N), and GPA1 was measured after a 2-h incubation in the presence of CaCl₂ or MgCl₂. Error bars, S.D.