Fig. 2. Expression of SI, SI_Q1098P and SI_Ala1-6 alanine scanning mutants in COS-1 cells at 37°C and 20°C. COS-1 cells were transiently transfected with the respective expression plasmids as indicated. Forty-eight hours after transfection the cells were pulsed with [³⁵S]methionine for 30 minutes at 37°C followed by different chase periods at 37°C or 20°C. After cell lysis, SI was immunoprecipitated with mAb anti-SI and the immunoprecipitates were treated with endo H, endo F/GF or left untreated. They were subjected to SDS-PAGE on 5% slab gels and analysed by phosphorimaging. For some gels, longer exposure was used because of the faint band intensity.