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Fig. 1. Association of IQGAP1 with the exocyst-septin complex is regulated by CDC42. (A) IQGAPs are conserved proteins. Domain structure of mammalian IQGAP1 (top) and yeast Iqg1p (bottom) with percent identity indicated on top of each domain. The sequences downstream of the GRD are 24% identical and are well-conserved across species. (B) IQGAP1, but not IQGAP2 (or IQGAP3, not shown), co-immunoprecipitates with the EXO70-SEPT2 complex. Antibodies against EXO70 and SEPT2 were used as indicated on the top of each lane to immunoprecipitate equal amounts of protein from pancreatic βTC-6 cells, and western blots were stained with monoclonal antibodies specific for IQGAP2 (middle panel) or IQGAP1 (right panel). Left panels: 5% of the input probed with the indicated antibodies is shown. `Mock' is a negative control using anti-Myc. (C) CDC42 disrupts the interaction between IQGAP1 and the exocyst-septin complex. βTC-6 stably expressing wild-type CDC42 (Cdc42WT) or the vector control were either treated with mastoparan (Mp +) to activate CDC42 or with vehicle alone as a control (Mp –), and their lysates were used for co-immunoprecipitation with anti-EXO70 monoclonal antibodies. Right panel: 5% of the proteins used for the IP is shown. The blots represent four experiments with identical results. CHD, calponin homology domain; IR, specific IQGAP repeats; WW, domain resembling the SH3 protein-interacting domains, not well-conserved in yeast; IQ, eight IQ motifs that bind calmodulin; GRD, rasGAP-related domain containing sequences that bind CDC42 and RAC1.
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