Marathon-Ready cDNA—made from high-quality poly A+ RNA and ligated to the Marathon Adaptor—is ready for 5'- and 3'-RACE PCR (Borson, Salo, and Drewes 1992). Marathon-Ready cDNA is a tissue-specific "pool" of premade double-stranded cDNA from which full-length transcript sequences can be amplified using gene-specific primers. It can also be used to study tissue-specific gene expression and to find polymorphic forms of mRNA, or mRNA belonging to a multigene family. This Marathon-Ready cDNA is synthesized from premium RNA derived from various rat tissues using a procedure optimized to produce full-length cDNA and to eliminate 3' heterogeneity (Chenchik, A., Diachenko, L., Moqadam, F., Tarabykin, V., Lukyanov, S., and Siebert 1996). After synthesis, blunt ends are created and the Marathon Adaptor is ligated to both ends of the double-stranded cDNA.