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 400 clones randomly selected from the subtracted cDNA library were electrophoresed in agarose gel and bound to nylon membranes. Duplicate membranes were hybridized with³²P-labeled cDNAs synthesized from poly(A)⁺RNA of +/+ (upper) or mi/mi (lower) CMCs. In the rightmost lanes, an equal amount of the β-actin cDNA fragment was 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 which hybridized to a greater degree with +/+ CMC-cDNAs than with mi/mi CMC-cDNAs, such as clones no. 5, 11, 232, 239, and 382, were selected, and subjected to DNA sequencing and a computer-assisted homology search. The identity of these clones is also shown by the clone number.