Comparison of E2F-complex DNA binding activity in extracts of human primary B cells and immature CD34⁺ hematopoietic cells. B cells and CD34⁺ cells were purified and whole cell extracts prepared as described in Materials and Methods. EMSA was then performed. Equal amounts of total cell lysate (8 μg) were incubated with a ³²P-labeled probe containing an E2F binding site and then separated on a 4% nondenaturing polyacrylamide gel. No whole cell extract was loaded in lane 1. Band ‘A’ was identified in quiescent B cells (lane 2) as previously described. Two bands were identified in CD34⁺ cells, ‘A,’ which comigrated with the band identified in B cells, and band ‘B’ (lane 3). These were confirmed as specific E2F complexes by competition with excess nonradioactive probe (lane 4).