Isothermal Nucleic Acid Amplification via Nick-Directing Primers
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Solution Overview
Problem
Current nucleic acid amplification methods, such as PCR and LCR, require temperature cycling, are limited by the need for stable enzymes and multiplexing capabilities, and suffer from contamination and low sensitivity, especially at low target concentrations, while isothermal methods like NDA face challenges with low amplification efficiency and selectivity.
Innovation Solution
The use of a reaction mixture containing forward and reverse external nick-directing primers, internal nick-directing primers, a strand-displacing DNA polymerase, and a nick-directing endonuclease, which allows for isothermal strand-displacement amplification through primer extension and strand-specific cleavage, enhancing amplification efficiency and rate via the Accelerated Cascade Amplification (ACA) method.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If PCR and LCR methods are used for nucleic acid amplification, then amplification capability is achieved, but temperature cycling apparatus and stable enzymes are required, increasing device complexity and operational difficulty
Solution Approach 1:
The invention changes the temperature parameter from cyclic variation to constant isothermal condition. The ACA method performs amplification at a single temperature (e.g., 37°C or 42°C) without requiring temperature cycling, thereby eliminating the need for complex thermal cycler apparatus while maintaining amplification capability through isothermal strand displacement and nicking mechanisms
Solution Approach 2:
The invention replaces the mechanical temperature cycling system with a biochemical system using strand-displacing DNA polymerase and nick-directing endonuclease. These enzymes naturally perform strand displacement and nicking functions at constant temperature, substituting the mechanical thermal cycling mechanism with a biochemical alternative that achieves the same amplification result without complex equipment
2Device complexity
If isothermal methods like NDA are used for amplification, then temperature cycling is eliminated, but amplification efficiency and selectivity are reduced
Solution Approach 1:
The invention segments the amplification process into distinct functional components: external ND-primers for initial binding, internal ND-primers for strand displacement, nick-directing endonuclease for cleavage, and strand-displacing polymerase for extension. This segmentation allows each component to perform its specific function efficiently at isothermal conditions, collectively achieving high amplification efficiency that overcomes the limitation of traditional NDA methods
Solution Approach 2:
The invention creates a composite enzymatic system combining strand-displacing DNA polymerase and nick-directing endonuclease that work synergistically. This composite system maintains high amplification efficiency at isothermal conditions by coordinating the activities of multiple enzymes with complementary functions, thereby overcoming the efficiency limitations of single-enzyme isothermal methods like NDA
3Productivity
If traditional amplification methods are used, then amplification is achieved, but sensitivity at low target concentrations is limited
Solution Approach 1:
The invention ensures continuous amplification action through isothermal conditions that prevent enzyme denaturation and maintain constant reaction kinetics. The strand-displacing polymerase and nick-directing endonuclease continuously perform their functions without the interruptions inherent in temperature cycling, resulting in sustained high-rate amplification that significantly enhances sensitivity for detecting low target concentrations
4Productivity
If multiple primers are used in amplification, then amplification rate increases, but selectivity and specificity may be compromised
Solution Approach 1:
The invention assigns different functional qualities to different primers: external ND-primers are designed for high-specificity binding to target sequences, while internal ND-primers are designed for strand displacement functionality. The nick-directing endonuclease is specifically engineered to recognize and cleave only at nick sites created by external ND-primers. This local differentiation of primer functions maintains high selectivity while enabling rapid amplification through the coordinated action of multiple primers with specialized roles
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
ACA achieves enhanced and synergistic amplification rates and efficiencies, overcoming limitations of existing methods by enabling efficient nucleic acid detection without the need for temperature cycling and improving sensitivity and selectivity across various target sequences.
Implementation Method 1
a nick-directing endonuclease for strand-specific cleavage of ND-primer-extension products
Implementation Method 2
a strand-displacing DNA polymerase, and deoxynucleoside 5'-triphosphates
Implementation Method 3
forward and reverse external nick-directing primers (ND-primers), at least one internal ND-primer
Data Source
AI summary
Particular aspects provide nucleic acid amplification and detection methods comprising: providing a reaction mixture containing a target nucleic acid with an amplifiable target sequence, forward and reverse external nick-directing primers (ND-primers), at least one internal ND-primer, a strand-displacing DNA polymerase, a nick-directing endonuclease for strand-specific cleavage of ND-primer-extension products, and deoxynucleoside 5′-triphosphates; and incubating the reaction mixture with reagents, and under conditions suitable to provide for amplification of the amplifiable target sequence, wherein the amplification comprises primer extension, by least one internal ND-primer, of an external ND-primer extension product comprising the amplifiable target sequence or a portion thereof but lacking the respective external ND-primer sequence or a portion thereof. Preferably, amplification comprises using a plurality of internal ND-primers, extension of one internal ND-primer extension product by a different internal ND-primer, and amplification is isothermal and synergistic with respect to the number of primers employed. Amplification and detection kits are provided.