Expression of c-myb in nuclear extracts of cell lines from various tissues. Protein (10 μg) from nuclear extract of the indicated cell lines was loaded in SDS sample buffer on a 7.5% Tris-HCl gel. After blotting, c-myb was detected using a monoclonal antibody (Upstate Biotechnology). Nuclear extract from Cos-7 cells transfected with a c-myb expression vector served as a positive control. A single band with a molecular weight of approximately 80 kD was detected for the nonmyeloid cell lines (PC3 and HeLa), whereas double bands were seen for the myeloid cell lines (U937 and KCL 22). This might indicate differences in the phosphorylation status or the presence of different splice variants.