<p><b>A and B.</b> HEK293 cells were transfected with FLAG-GCH1 or empty vector (control) for 2 days and treated with the 26S proteasome inhibitors MG132 or lactacystin (Lac, irreversible inhibitor) for 6 hours. Lysates from cells expressing FLAG-GTPCH1 were immunoprecipitated with anti-FLAG resin and immunoblotted using the indicated antibodies. HEK293 transfected with empty vectors were used as a negative control. The asterisk (*) indicates IgG bands. <b>C.</b> HEK293 cells were co-transfected with FLAG-GCH1 and HA-Ub plasmids and treated with or without MG132 for 6 hours. Lysates from cells expressing FLAG-GTPCH1 were immunoprecipitated with anti-FLAG resin and immunoblotted with the FLAG, HA, or β-actin antibodies. The blot shown is representative of three independent experiments.</p
