Chemical Capping for Template Switching Bias Reduction
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Solution Overview
Problem
Current template-switching (TS) methods face challenges in efficiently capping RNAs without a 5' terminal phosphate and in reducing bias in RNA representation, particularly for microRNAs and degraded/fragmented DNAs, due to discrimination by reverse transcriptases based on 5' terminal nucleotides.
Innovation Solution
A method involving chemical capping of polynucleotides with a 5' monophosphate using activated nucleoside 5' mono- or poly-phosphates, forming a 5' to 5' polyphosphate linkage, which allows for the capping of RNAs and DNAs, including those with no terminal phosphate, and reduces bias by using a guanosine triphosphate cap, enhancing template switching efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If enzymatic capping is used for RNAs with diphosphate or triphosphate, then capping efficiency is improved, but RNAs with single phosphate or no phosphate cannot be capped
Solution Approach 1:
The invention changes the chemical parameters of the capping reagent from enzyme-specific substrates to chemically activated nucleoside phosphates that can react with various phosphate states. The activated phosphate group enables direct chemical reaction with the 5' end of RNAs regardless of their initial phosphate status, expanding adaptability while maintaining efficiency.
Solution Approach 2:
The invention replaces the biological enzymatic system with a chemical reaction system. Instead of using Vaccinia Capping Enzyme that requires specific substrate recognition, the patent employs chemically activated nucleoside phosphates that undergo direct chemical reactions with RNA 5' ends, eliminating enzyme-substrate specificity constraints.
2Adaptability or versatility
If template switching is performed with RNAs having different terminal nucleotides, then comprehensive RNA coverage is achieved, but bias in representation occurs due to RT discrimination
Solution Approach 1:
The invention performs preliminary chemical capping of the RNA 5' end before template switching occurs. This pre-modification creates a uniform structure that all reverse transcriptases can recognize and process equally, eliminating sequence-dependent discrimination that would otherwise cause representation bias in the final library.
3Adaptability or versatility
If chemical capping with activated nucleoside phosphate is used, then RNAs with single phosphate or no phosphate can be capped, but reaction conditions must be optimized
Solution Approach 1:
The invention optimizes chemical parameters including pH (5.0-7.0 range), temperature (4°C-37°C range), and molar ratios of reagents to create a robust reaction system. These optimized parameters enable the capping reaction to proceed efficiently under mild conditions without requiring complex equipment or multi-step procedures.
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
The method significantly improves the efficiency of template switching and reduces bias in cDNA representation, achieving at least a 2-fold increase in cDNA yield and uniformity across different 5' terminal nucleotides, enabling accurate analysis of diverse RNA and DNA populations.
Implementation Method 1
The activated nucleoside 5' mono- or poly-phosphate may include an imidazole moiety where a nucleophilic substitution reaction displaces the imidazole
Data Source
AI summary
Provided herein is a method for chemically capping polynucleotides having a 5′ monophosphate. In some embodiments the method may comprise: combining an activated nucleoside 5′ mono- or poly-phosphate with a population of polynucleotides that comprises polynucleotides having a 5′ monophosphate, to produce a reaction mix; and incubating the reaction mix to produce reaction products that comprise a polynucleotide and a 5′ nucleoside cap, linked by a 5′ to 5′ polyphosphate linkage. The chemical capping method described herein can be incorporated into a variety of cDNA synthesis methods.