Nucleic Acids Research, 2003, Vol. 31, No. 19 e117
© 2003 Oxford University Press
Real-time closed tube single nucleotide polymorphism (SNP) quantification in pooled samples by quencher extension (QEXT)
MATFORSK Norwegian Food Research Institute, Osloveien 1, 1430 Ås, Norway
*To whom correspondence should be addressed. Tel: +47 64 97 01 00; Fax: +47 64 97 03 33; Email: knut.rudi{at}matforsk.no
Quencher extension (QEXT) is a novel single step closed tube real-time method to quantify SNPs using reporters and quenchers in combination with primer extension. A probe with a 5'-reporter dye is single base extended with a dideoxy nucleotide containing a quencher dye if the target SNP allele is present. The extension is recorded from the quenching (reduced fluorescence) of the reporter dye. This avoids the influence of the unincorporated dye-labeled nucleotides, resulting in high accuracy and a high signal-to-noise ratio. The relative amount of a specific SNP allele is determined from the nucleotide incorporation rate in a thermo-cycling reaction. We tested the QEXT assay using five SNPs in the Listeria monocytogenes inlA gene as a model system. The presence of the target SNP alleles was determined with high statistical confidence (P < 0.0005). The quantitative detection limits were between 0 and 5% for the targeted SNP alleles on a background of other SNP alleles (P < 0.05). The QEXT method is directly adaptable to current real-time PCR equipment and is thus suited for high throughput and a wide application range.
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