Fig. 2. Levels of exogenous protein expression: western blot analysis of supernatants of stably transfected F9 teratocarcinoma cells with a mouse monoclonal antibody detecting the FLAG tag shows approximately equal expression of both constructs, 1III3-5 and 1V1-3. As a control, F9 cells carrying the empty expression vector were analysed. For normalization of the loading of secreted proteins, a rabbit polyclonal antibody against the mouse BM40 protein was used. The two blots shown are derived from the same gel.