Helicase-dependent amplification of circular nucleic acids

A method for amplifying a target DNA sequence in a cDNA, comprising:

• (a) providing the cDNA;
• (b) contacting the cDNA with a first sequence specific oligonucleotide primer that hybridizes to one strand of the cDNA and a second sequence specific oligonucleotide primer that is substantially identical to a portion the one strand of the cDNA, a helicase preparation, a DNA polymerase, and dNTPs;
• (c) replicating the cDNA under conditions whereby the first primer is extended around the circle repeatedly to generate a single strand linear concatemer, and whereby the second primer hybridizes to multiple sites on a complementary single-stranded DNA which generate extension products for continuing synthesis of the target DNA sequence and the cDNA;
• and
• (d) amplifying the target cDNA.

A method for amplifying a target DNA sequence in a cDNA, comprising:

• (a) annealing a first sequence specific oligonucleotide primer to a first DNA sequence adjacent to or within a target DNA sequence in a cDNA in the presence of a polymerase and a helicase preparation to synthesize by primer extension, a displaced single stranded DNA containing a plurality of copies of the target DNA sequence;
• (b) annealing a second specific oligonucleotide primer to the displaced strand of DNA at specific sites for synthesizing by primer extension, a plurality of complementary single stranded DNA concatamers, each concatamer including the target DNA sequence and each concatemer forming a substrate for multiple rounds of displacement synthesis from the first or second primer;
• and
• (c) amplifying the target DNA sequence.