The transcript contains 2 polyadenylation signals, and the deduced protein contains 1,542 amino acids and has a calculated molecular mass of 170 kD. SETBP1 contains a central SKI homology region and a C-terminal SET-binding domain that is followed by 3 sequential PPLPPPPP repeats. SETBP1 also has 3 bipartite nuclear localization signals, 6 PEST sequences, 4 KxKHKxK repeats, 8 LSxxL repeats, and 10 PxxPS repeats. Northern blot analysis detected a major 5.8-kb transcript in all tissues and cell lines examined. Immunofluorescence analysis detected fluorescence-tagged and endogenous SETBP1 predominantly in nuclei of human cell lines.Immunoprecipitation analysis verified that SETBP1 interacted with endogenous SET in a human osteosarcoma cell line.