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Target sequence heterogeneity causes the 'hook effect' in fluorescent dye-based quantitative PCR.

Kristina Warton^1,2, Yue Xu³, Caroline Elizabeth Ford¹

¹School of Women's & Children's Health, University of New South Wales, Sydney, NSW, Australia.

|June 6, 2020

Summary

The hook effect in quantitative PCR (qPCR) is caused by amplifying similar DNA targets. These targets form heteroduplexes, reducing fluorescence in later qPCR cycles.

Keywords:

hook effect optimization quantitation quantitation artifact quantitative PCR

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Area of Science:

Molecular Biology
Genetics
Biochemistry

Background:

The hook effect in quantitative PCR (qPCR) is characterized by a decrease in fluorescence signal after an initial amplification phase.
This phenomenon can lead to inaccurate quantification in molecular assays.

Discussion:

We propose the hook effect in intercalating dye-based qPCR results from amplifying heterogeneous, related DNA targets.
The observed fluorescence decrease is attributed to the formation of DNA heteroduplexes between related amplicons.
These heteroduplexes have a lower melting temperature, causing them to dissociate and reduce fluorescence signal at the measurement temperature.

Key Insights:

The hook effect is mechanistically linked to the amplification of homologous DNA sequences.
Heteroduplex formation and subsequent dissociation below the assay's measurement temperature explain the fluorescence drop.
This mechanism was experimentally validated using qPCR targeting repetitive Alu elements.

Outlook:

Understanding the hook effect is crucial for accurate qPCR assay design and interpretation.
Further studies could explore strategies to mitigate or control the hook effect in complex DNA samples.
Investigating this phenomenon in other repetitive DNA families could broaden its applicability.