Fig. 7. Binding of HA to GRC-transfected COS-7 cells, but not to GRC itself. (A) Mock- and GRC-transfected COS-7 cells were incubated with ¹²⁵I-HA bipeptide (1.3x10⁶ cpm/ml) for 30 minutes at 37°C. After fixation with 4% formaldehyde in 7% acetic acid and 7% glycerol, slides were covered with dipping film and developed for autoradiography 8 days later. Shown on the left are phase-contrast and on the right bright field micrographs. (B) ¹²⁵I-HA bipeptide was crosslinked to GRC-FLAG or mock-transfected COS-7 cells by EDC and sulfo-NHS. Membrane fractions were solubilized, and subjected to pull-down with anti-FLAG agarose. GRC was recovered quantitatively in the immunoprecipitate, but contained no radioactive HA. (HA-AR, HA autoradiography).