Fig. 2. UV-exposed cells did not reveal increased phosphate incorporation in the EGF receptor. In vivo labelling of cells were performed by preincubation of cells with phosphate-free medium (MEM) for 2 hours, followed by incubation with [³²P] orthophosphate in DMEM for 2 hours. Cells were then left untreated or exposed to UV or EGF, and incubated for the indicated time intervals. Cell lysates were subject to immunoprecipitation with an anti-EGFR-protein G-sepharose conjugate. The EGFR immunoprecipitates were separated by SDS-PAGE, and identified by (A) autoradiography and (B) western immunoblotting with anti-EGFR. Cells stimulated with 5 nM EGF for 5 minutes were used as positive controls. C and E denote control and EGF-stimulated cells, respectively. The molecular weight markers presented at the left indicate 220 kDa.