Fig. 9. Secretion of FGF-2 from CHO K3 cells occurs as efficiently as from parental CHO wild-type cells. Parental CHO wild-type (lanes 1-3) and CHO K3 mutant cells (lanes 4-6) expressing HASPB-N18-GFP were transduced with retroviral particles containing the FGF-2-GFP open reading frame controlled by a doxicycline-dependent element. Transduction efficiency was about 65% as determined by GFP-derived fluorescence. Both cell types were treated with a membrane-impermeable biotinylation reagent. Cell lysates were generated and biotin-labeled and biotin-unlabeled proteins were separated by streptavidin affinity chromatography. Input material (lane 1 and 4; 4%), streptavidin supernatant (non-biotinylated proteins, lanes 2 and 5; 4%) and streptavidin-bound proteins (biotinylated proteins, lanes 3 and 6; 50%) were separated on SDS gels followed by western blotting using affinity-purified anti-GFP antibodies.