(A) Expression of p130 in human primary CD34⁺ hematopoietic cells. Purified CD34⁺ cells were induced to proliferate by the addition of cytokines as previously described in Materials and Methods. Samples were taken at 0 hours, 8 hours, and every 4 hours thereafter until 20 hours and then every 12 hours up to 4 days and lysed in SDS lysis buffer. Equal amounts of total cell lysate (equivalent to 2 × 10⁵cells) were subjected to SDS-PAGE and Western blotting. The hyperphosphorylated form of p130 (pp130) is present at 8 hours and accumulates thereafter. (B) Expression of p107 and pRb in human primary CD34⁺ hematopoietic cells. Purified CD34⁺ cells were induced to proliferate by the addition of cytokines and samples were taken at 24-hour intervals until 96 hours. Western blotting was performed using specific polyclonal antibodies that recognized p107 and pRb. The hyperphosphorylated forms of both proteins are arrowed and are detectable at 1 day and then accumulate over the next 3 days as the cells proliferate.