Absence of CSF-1R expression in p19-inducible 32D cells. (A) Parental 32D cells and the p19-inducible 2C subclone were grown in medium containing IL-3 in the presence or absence of zinc for 4 days, as indicated at the top of the panel. BAC1.2F5 macrophages were grown in medium containing CSF-1. Cells metabolically labeled for 90 minutes with [³⁵S]-methionine were lysed and precipitated with nonimmune rabbit serum (NRS), or with rabbit antisera directed to human CSF-1R (c-fms ) or to the feline v-fms oncogene product, as indicated below the panel. The precipitated labeled proteins were electrophoretically separated on denaturing polyacrylamide gels and detected by autoradiography (exposure time 36 hours). The position of CSF-1R is indicated at the right. (B) RNAs extracted from the same cells as in A were copied into DNA by reverse transcription and amplified by PCR using internal primers based on the mouse CSF-1R cDNA sequence. For two reactions, RNA from CSF-1R-positive BAC1.2F5 cells (lane 6) was mixed as 1% (lane 4) and 5% (lane 5) of the total together with RNA extracted from subclone 2C cells that had been grown in the presence of zinc. RT-PCR products were separated on nondenaturing agarose gels using markers of known complexity (lane M). The position of the expected 554 base-pair CSF-1R product is indicated at the right.