Screening of +/+ CMC-specific clones by Southern blot analysis. After digestion with both Sma I and Not I to separate the cDNA insert, plasmid DNAs of 80 clones randomly selected from the subtracted cDNA library [(+/+-mi/mi) or (+/+-tg/tg)] were electrophoresed in 1.0% agarose gel (left panel, stained with ethidium bromide [EdBr]) and bound to nylon membranes. Duplicate membranes were hybridized with³²P-labeled cDNAs synthesized from poly(A)⁺RNA of +/+ (middle panel), mi/mi (right upper panel), ortg/tg (right lower panel) CMCs. In some lanes, an equal amount of the mouse β-actin (A) and human GAPDH (G) cDNA fragments and a λ-BstEII size marker (M) were loaded as a control, and we graphically equalized the intensity of their bands for two filters to normalize the intensity of other sets of the bands. The clones that hybridized to a greater degree with +/+ CMC cDNA than withmi/mi or tg/tg CMC cDNA were identified by arrowheads with numbers.