Expression of WT and mutant G-CSF receptors. (A) Schematic representation of the intracellular domain of the G-CSF receptor and mutants. Boxes 1 and 2 represent subdomains conserved in the hematopoietin receptor superfamily. The open box indicates the deleted region in G-CSF-R–d749-769 and G-CSF-R–d715-735. (B) Flow cytometric analysis of the expression levels of the different G-CSF-R forms used in luciferase reporter assays. Open histograms indicate cells stained with biotinylated G-CSF-R antibodies and phycoerythrin-conjugated streptavidin (SA-PE); shaded histograms, cells stained with SA-PE only; and e.v., cells transfected with empty vector.