Sulfonated Cytosine Carry-Over Protection in DNA Methylation
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Solution Overview
Problem
Current methods for DNA methylation analysis using bisulfite conversion face challenges in preventing carry-over contamination, as bisulfite-treated DNA contains uracils, making it incompatible with standard uracil-DNA-glycosylase (UNG) based decontamination methods.
Innovation Solution
The method involves sulfonating unmethylated cytosines without subsequent desulfonation, allowing uracil-DNA-glycosylase to degrade non-sulfonated uracil-containing DNA while sparing sulfonated uracils, thereby providing a means to differentiate between methylated and unmethylated cytosines and prevent contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bisulfite conversion is used to differentiate methylated and unmethylated cytosines, then methylation analysis capability is improved, but carry-over contamination cannot be prevented because the treated DNA contains uracils
Solution Approach 1:
The patent introduces a localized chemical modification (sulfonation at C6 position) that creates a spatial distinction between template DNA and carry-over contaminants. The sulfonated uracils in template DNA have different properties from non-sulfonated uracils in contaminants, allowing selective degradation by UNG enzyme while preserving template integrity for subsequent amplification
Solution Approach 2:
The C6-sulfonated uracil acts as an intermediary structure that bridges the template DNA and the UNG enzyme system. This modified uracil structure is recognized by UNG but cannot be degraded, creating a protective effect that allows the enzyme to remove non-sulfonated uracils from contaminants while leaving the sulfonated template intact
2Reliability
If standard UNG-based decontamination is applied to bisulfite-treated DNA, then carry-over contamination is prevented, but the template DNA is degraded because it contains uracils
Solution Approach 1:
The patent introduces a localized chemical modification (sulfonation at C6 position) that creates a spatial distinction between template DNA and carry-over contaminants. The sulfonated uracils in template DNA have different properties from non-sulfonated uracils in contaminants, allowing selective degradation by UNG enzyme while preserving template integrity for subsequent amplification
Solution Approach 2:
The sulfonation of uracils in template DNA occurs before the UNG treatment step, creating a protective modification in advance. This preliminary action prevents the template DNA from being degraded by UNG, while still allowing the enzyme to degrade non-sulfonated uracils in carry-over contaminants
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 enables reliable carry-over protection in DNA methylation analysis by ensuring only the legitimate template is amplified, while sulfonated uracils remain intact, allowing for accurate methylation status determination without destroying the template DNA.
Implementation Method 1
incubating a template nucleic acid with a bisulfite reagent containing solution, whereby the unmethylated cytosines within said nucleic acid are sulfonated
Implementation Method 2
adding to this mixture UNG and incubating the mixture, whereby nucleic acids containing non-sulfonated uracils are degraded
Implementation Method 3
treating the sulfonated or sulfonated and deaminated template nucleic acid with uracil-DNA-glycosylase (UNG), which degrades all nonsulfonated-uracil-containing DNA
Implementation Method 4
terminating the UNG activity, and desulfonating the template nucleic acid
Data Source
AI summary
Particular aspects provide methods for specific amplification of template DNA in the presence of potentially contaminating PCR products from previous amplification experiments. Particular embodiments comprise, in a first step, contacting DNA with a bisulfite solution, which sulfonates unmethylated (but not methylated) cytosines, resulting in cytosine deamination and generation of sulfonated uracil. Such sulfonation protects the template nucleic acid from being a target for the enzyme uracil-DNA-glycosylase (UNG), whereas any contaminating DNA, which contains unprotected unsulfonated or desulfonated uracils, is degraded enzymatically while the UNG is active. After UNG treatment and inactivation thereof, the sulfonated uracil bases are converted into uracil by desulfonation. Such aspects have substantial utility for decontamination of nucleic acid samples; e.g., for avoiding amplification of ‘carry over products’ in the context of DNA methylation analysis. In further aspects, the inventive methods can be generally used as simplified methods of bisulfite treatment.