Fig. 4. Characterization of EphB1 mutants lacking the caveolin-binding motif. (A) Relative mRNA expression of EphB1 mutant and wild-type (wt) receptors was detected using real-time RT-PCR (numbers correspond to mutant and wt receptors listed at the bottom of the figure; for further details of the mutants, see text). The total RNA isolation was performed using Trizol® reagent. The 18S steady-state mRNA level was used as reference. The results showed that all of the EphB1 receptor constructs were expressed at the mRNA level. (B) ELISA was performed using the ephrinB2/Fc chimera to detect EphB1 expression on the cell membrane. The binding of the chimera was detected using AP-conjugated secondary antibody and color reaction was initiated by the addition of p-nitrophenyl phosphate. There was no detectable cell-surface expression of any of the mutant receptors when compared with CHO cells transfected with wild-type EphB1 receptor or with CHO-EphB1 cells. Results are representative of at least three independent experiments.