Fig. 5. (A) The interaction of the semi-CRIB motif of Par6 with its PDZ domain. As in Figure 3, dotted black lines represent salt bridges and hydrogen bonds. Non-sequence-specific hydrogen bonds (e.g., the main chain hydrogen bonds of the β-sheet) are not shown for clarity. (B) The interactions of Par6 with the Switch I and II regions of Cdc42. (C) Effect of Par6 and PAK GBD domains on the intrinsic GTPase activity of Cdc42. Cdc42 loaded with [γ-³²P]GTP was incubated for 10 min plus saturating concentrations (20× K_d) of the GST–GBD fusion proteins or GST alone. The Cdc42 was then bound to filters, washed to remove free ³²P-phosphate and counted.