CHO cells were transiently transfected with vector alone, V5-rat SR-BI or the indicated mutants. Thirty-six hours post-transfection, cells were incubated with a culture medium containing 50 μg protein/ml of [125I-DLT]-[3H]COE-labeled hHDL3 for 5h. At the end of incubation, the cells were processed for the determination of [125I-DLT]-hHDL3 binding activity and the quantification of selectively internalized HDL-[3H]COE as described under “Materials and Methods.” The results are Mean ± SE at least three independent experiments and normalized to per unit of total expressed SR-BI. A, selective HDL-CE uptake and B,HDL binding activity.