Northern blot analysis of α chain of GM-CSFR and of β actin in ECs and in U937 cell lines. Seven micrograms of PolyA⁺ RNA was run in a formaldehyde-agarose gel and after blotting to Duralon membrane, hybridized to α-chain– and β-actin–specific probes. Transcripts have been visualized by autoradiography. This experiment is representative of three performed with similar results.