Fig. 4. Identification of interacting domains of CSP and G proteins. (A) Schematic representation of CSP and its deletion mutants encoded by the GST fusion cDNA constructs. (B) These fusion proteins were immobilized on glutathione-agarose beads and incubated with homogenate at 37°C for 30 minutes. The beads were washed, and bound proteins were eluted in sample buffer, fractionated by SDS-PAGE and subjected to western blot analysis. The nitrocellulose membrane was probed with anti-G_ß monoclonal and anti-G polyclonal (Calbiochem) and anti-G_i polyclonal (Santa Cruz) antibodies. (C) Coomassie staining profile of CSP-GST and its truncation mutants. Note that CSP truncation mutants 83-198 and 137-198 migrate anomalously on SDS-PAGE. These results are representative of four independent experiments.