Schematic diagram of the normalized-subtracted cDNA preparation protocol. (A) general scheme for preparing full-length single-strand cDNA; (B) representation of various populations of tester cDNAs; (C) normalizing driver (cellular mRNA) and subtracting drivers (run-off transcripts); (D) hybridization; (E) rare/new cDNAs are used for second-strand cDNA preparation (normalized/subtracted cDNA library); (F) abundant cDNAs/unwanted cDNAs are removed and may be used for the preparation of minilibraries to implement subtraction.