Marathon-Ready cDNA—made from high-quality poly A+ RNA and ligated to the Marathon Adaptor—is ready for 5'- and 3'-RACE PCR (Chenchik et al. 1996). 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 mouse tissues using a procedure optimized to produce full-length cDNA and to eliminate 3' heterogeneity (Borson et al. 1992). After synthesis, blunt ends are created and the Marathon Adaptor is ligated to both ends of the double-stranded cDNA.