Expression of mammalian Pc-G genes in purified bone marrow CD34⁺ subpopulations. Five to ten thousand cells were isolated from each subpopulation (>98% purity upon reanalysis) and their total RNA was reverse-transcribed and PCR-amplified as described in the Materials and Methods. From primitive to mature subpopulations: subpopulation I, CD34⁺CD45RA⁻CD71⁻; subpopulation IIM, CD34⁺CD45RA⁺CD71^lo; subpopulation IIIE, CD34⁺CD45RA⁻CD71^hi and CD34⁻ cells. Exposure times (all at −70°C unless specified) were as follows: HP1^Hsα, 6.5 hours at room temperature; HP1^Hsγ, 1.2 hours; M31, 6 days; M32, 27 hours; M33, 26 hours; Mel-18, 24 hours; BMI-1, 8 days; Mph-1/Rae-28, 3 days;ENX-1, 4.5 hours; β-globin, 5 minutes; and β-actin andCD34, 5 hours each.