The isolation of full-length cDNAs remains a frequent task undertaken in many laboratories. A full-length cDNA is often desirable for one of the following purposes: 1) to complete the sequence of a partial cDNA cloned by library screenings or the yeast one- or two-hybrid system; 2) to derive the cDNA sequence encoding a protein, based on peptide sequences; 3) to obtain the sequence of a reported cDNA for functional analysis or expression studies; and 4) to define exon/intron boundaries of a cloned gene or determine transcription start site(s) of a promoter.