Fig. 5. UV-exposed cells showed no induced polyubiquitination of the EGF receptor. Cells were either left untreated or treated with 5 nM EGF or 200 J/m² UV, and incubated for the indicated time intervals (minutes). (A) The cell lysates were subject to SDS-PAGE and western immunoblotting with anti-EGFR. Polyubiquitination, identified as smears, was observed only in EGF-stimulated cells incubated for 1-10 minutes (arrows). The molecular weight marker presented at the left indicates 220 kDa. (B) Cells were either left untreated or exposed to 200 J/m² UV or 5 nM EGF, and incubated for 10 minutes before immunoprecipitation with anti-Cbl. The immunoprecipitates were subjected to SDS-PAGE and western immunoblotting with either anti-Cbl (left) or anti-pTyr (right). C, U and E denote control, UV-exposed and EGF-stimulated cells, respectively. The molecular weight markers presented at the left indicate 220 and 96 kDa.