Patent ID: 7662556

Claim:
A method of obtaining a full-length cDNA comprising: (a) isolating a full-length mRNA; (b) attaching a double-stranded DNA tag to the 5′ end of the isolated mRNA wherein the DNA tag is covalently linked to a topoisomerase and wherein the topoisomerase is released upon attachment of the DNA tag, wherein the double-stranded DNA tag comprises an upper strand and a lower strand, wherein the upper strand comprises a 5′ tail, and wherein the lower strand comprises a 1 to 4 nucleotide overhang at its 5′ end, wherein the overhang has a sequence which is complementary to and base pairs with a sequence of 1-4 nucleotides at the 5′ end of the isolated mRNA; (c) contacting the DNA tagged mRNA from step (b) with a reverse transcriptase under the conditions which permit reverse transcription so as to thereby obtain a DNA-RNA molecule; and (d) subjecting the DNA-RNA molecule from step (c) to a polymerase chain reaction (PCR) so as to obtain the full-length cDNA.