Figure 4.

Mutation of the glutamic finger of Sec7d increases the rate of BFA binding. Association kinetics of [³H]BFA (15 μM) with 0.5 μM [YSDM]Arno-Sec7 (white symbols) or [YSDN-E156K]Arno-Sec7 (■), in the presence of 0 (×), 1 (○), 2 (■, □), or 5 μM (▵) [Δ17]ARF1–GDP. The reaction was initiated by the addition of Sec7d. The t = 0 point corresponds to the initial level of bound [³H]BFA just before the addition of Sec7d and represents the nonspecific binding of BFA. Bound radioactivity was determined on 15-μl aliquots (7.5 pmol of Sec7d).