(A) Normal and PU.1−/− myeloid colonies contain cells that express GM-CSF receptor  (GMR). A 1:10 dilution of an affinity purified rabbit polyclonal antibody to a cytoplasmic portion of GMR was used to stain pooled normal or PU.1−/− colonies. The same concentration of preimmune rabbit control antibody was also used. (B) The expression of GMR was verified by reverse transcriptase–PCR (RT-PCR). Normal (N) and PU.1−/− colonies were harvested, and total RNA was extracted. Two micrograms of total RNA was used for cDNA synthesis and PCR. Expression of both GMR and PU.1 was examined. PCR conditions: 94°C 1", 60°C 1", and 72°C 2", for 40 cycles. A no-cDNA control (C) was included in this assay.