Figure 3.

Requirement of RacB for chemoattractant-mediated PAKc activation, F-actin polymerization, and myosin II assembly. (A) RNA blot of wild-type and racB null cells probing for the RacB coding region (Supplementary Figure S1). The lower portion of the blot depicts the rRNA and shows equal loading. (B) cAMP-stimulated kinase activity of myc-PAKc expressed in wild-type and racB null cells. Aggregation-competent cells were stimulated with cAMP and kinase activity was measured as described in Materials and methods. The lower panel depicts the Western blot probed with the anti-myc antibody and indicates the amount of PAKc in each immunoprecipitate. pH2B is ³²P-labeled phosphorylated Histone 2B. (C, D) Kinetics of F-actin polymerization and myosin II assembly, respectively, in the Triton-insoluble, cytoskeletal fraction of wild-type and racB null cells.