RNase protection analysis with the 656-bp Nde/Nci probe (residues 2751 to 3407). RNA from 19 of 23 samples protects a full-length fragment, indicating 656 bp of sequence homology with the KB C-1 cDNA from which this probe was derived. RNA from three samples (bold) protects two additional fragments of 412 bp and 244 bp in length as a result of a mismatch at 2995 (similar results in DLD-1, RNA not shown). Vb, vinblastine; Ad, adriamycin.