We next characterized IRAS mAb ability to recognize IRAS proteins in their native states by immunoprecipitation. Cell extracts were immunoprecipitated with the mAb DA041 and analyzed with mAb DA041 immunoblotting after 48-hour transfection with PCMV-myc-IRAS. IRAS was selectively immunoprecipitated from cell lysates that expressed the myc-IRAS protein (approximately 175 kDa), and those which corresponded to the predicted size of the full-length IRAS ( Figure 4) . Immunoprecipitation of lysates with mouse normal IgG did not result in detection of protein species. Lysates were immunoprecipitated with the c-myc mAb to confirm mAb specificity, and similarly sized bands were detected. No corresponding band was visualized when the negative control c-myc mAb was used to immunoprecipitate cell lysate of the transfectant expressing the empty PCMV-myc vector. Similar results were obtained with the mAbs DD015 and BE073 under the same conditions, and the remaining mAbs BA022 and AH021 scored negatively. Therefore, the 3 isolated antibodies specifically recognized native full-length IRAS protein products.