Fig. 3. The N-terminal region of Grg4 interacts with the transactivation domain of Pax5. (A) Interaction of Pax5 and VP16-Grg4. The expression plasmids indicated (100 ng) were co-transfected into J558L cells together with the Renilla luciferase gene pRL-SV40 (0.4 µg) and firefly luciferase gene luc-CD19 (5 µg; Dörfler and Busslinger, 1996). After 48 h, the cells were lysed, luciferase activities were measured, and the activity of the firefly luciferase was standardized relative to the control Renilla luciferase to normalize for differences in transfection efficiencies. Luciferase values are shown relative to the activity measured with the empty expression vector pKW2T (left bar). (B) Interaction of the Q domain of Grg4 with the transactivation domain of Pax5. Both luciferase genes and the Pax5 expression plasmids indicated (100 ng each) were electroporated into J558L cells with (hatched bars) or without (black bars) the VP16-Grg4 expression vector (100 ng). Average values of three experiments are shown.