Sequence analysis and functional studies of interleukin-3 receptor alpha subunit-encoding cDNAs amplified from KG-1 leukemic cells and normal human marrow.

Two partial cDNAs encoding the human interleukin-3 receptor alpha subunit (IL-3R alpha) were cloned from KG-1 leukemic cells using the polymerase chain reaction. Sequence analysis of these cDNAs predicted two single-amino-acid (aa) changes as compared with the published TF-1 leukemic cell IL-3R alpha sequence [Kitamura et al., Cell 66 (1991) 1165-1174]. These changes were confirmed by sequence analysis of a second set of independently derived cDNAs. Identical aa changes were found in the IL-3R alpha encoded by cDNAs cloned from normal CD34+ human marrow cells. Ligation of the partial cDNAs derived from KG-1 cells resulted in a full-length functional IL-3R alpha cDNA clone. Deletion of the extracellular 'LSXWS' consensus sequence resulted in complete loss of detectable [125I]IL-3 binding when this mutant receptor was co-expressed in COS-7 cells with the beta subunit of the IL-3 receptor.