RhPCR Primer Design for DNA Variant Detection
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Solution Overview
Problem
Existing methods for detecting DNA mutations, such as SNPs and indels, face challenges in discrimination efficiency and error reduction, particularly due to the limitations of wild-type DNA polymerases and primer-dimer artifacts.
Innovation Solution
The use of high discrimination polymerase mutants and blocked-cleavable RNase H2-dependent PCR (rhPCR) primers allows for improved mismatch discrimination, enabling the placement of mismatches 5′ of the RNA and reducing primer-dimer formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If wild-type DNA polymerases are used for mismatch detection, then the PCR reaction can proceed with standard enzymes, but the discrimination capability is limited due to low mismatch detection ability
Solution Approach 1:
The patent introduces RNase H2 as an intermediary enzyme that performs mismatch discrimination. Instead of relying on the DNA polymerase's inherent mismatch detection ability, the system uses RNase H2 to cleave RNA-DNA hybrids at mismatched sites, thereby transferring the discrimination function from the polymerase to this specialized nuclease.
Solution Approach 2:
The patent modifies the biochemical parameters of the PCR system by incorporating blocked-cleavable primers with RNA-DNA hybrid regions. These primers are designed with specific properties: a 5' RNA segment that can be cleaved by RNase H2, a blocking group that prevents extension, and a DNA segment that hybridizes to the template. This parameter change enables the system to achieve high discrimination while maintaining standard polymerases.
2Measurement precision
If the mismatch is placed near the 3' end of the primer for RNase H2 cleavage, then discrimination is improved, but the polymerase cannot be relied upon for discrimination after cleavage and repeated interrogation is required
Solution Approach 1:
The patent extracts the discrimination function from the polymerase activity and places it solely in the RNase H2 cleavage step. By designing the mismatch to be immediately adjacent to the RNA segment, the system ensures that RNase H2 performs the discrimination in a single cleavage event, eliminating the need for repeated polymerase-based interrogation cycles.
Solution Approach 2:
The blocked-cleavable primer design performs preliminary discrimination before the polymerase extension step. The RNA segment is positioned such that RNase H2 can cleave it based on mismatch presence, and the blocking group prevents further extension until the RNA is removed. This preliminary action separates the discrimination step from the amplification step, improving both precision and efficiency.
3Reliability
If standard PCR primers are used, then the assay can be performed with conventional reagents, but primer-dimer artifacts are generated that reduce detection accuracy
Solution Approach 1:
The patent converts the potential harm of primer-dimer formation into a beneficial feature. The blocked-cleavable primer design with 5' RNA segments and blocking groups prevents primers from annealing to each other (forming dimers) because the blocking group sterically hinders hybridization. The RNA segment that would otherwise be susceptible to degradation is instead used as a discrimination element by RNase H2, turning a vulnerability into an advantage.
Solution Approach 2:
The patent applies local quality modification to the primer structure by adding distinct functional regions: a 5' RNA segment with blocking group for discrimination and artifact prevention, and a 3' DNA segment for template hybridization. This localized functional differentiation ensures that the primer performs multiple roles: specific binding, mismatch detection, and artifact prevention, all within a single molecular structure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in a more efficient and less error-prone method for detecting DNA mutations, with enhanced discrimination capabilities and reduced primer-dimer artifacts, facilitating accurate SNP and indel detection.
Implementation Method 1
the mismatch sensitivity of the RNase H2 enzyme in rhPCR allows for both sensitive detection of DNA mutations, and elimination of primer-dimer artifacts from the reaction
Implementation Method 2
the DNA polymerase performs the mismatch discrimination by detection of a mismatch at or near the 3′ end of the primer
Data Source
AI summary
The invention can be used to provide a more efficient and less error-prone method of detecting variants in DNA, such as SNPs and indels. The invention also provides a method for performing inexpensive multiplex assays.