Cell-Free Circular DNA Amplification via Theta Replication
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Solution Overview
Problem
Current methods for amplifying circular DNA in vitro are inefficient, requiring primers, producing linear DNA, and limiting the amplified DNA size to a few kbp, with low replication efficiency and difficulty in amplifying long circular DNA.
Innovation Solution
A cell-free system involving a reaction mixture with a first enzyme group for circular DNA replication, a second enzyme group for Okazaki fragment maturation and catenane formation, and a third enzyme group for separation of sister circular DNAs, along with essential nucleotides and ions, to achieve exponential amplification of circular DNA.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If rolling circle amplification is used to amplify circular DNA, then amplification can be performed in vitro, but a primer specific to the target DNA must be designed each time and the amplification product is linear DNA requiring additional cyclization steps
Solution Approach 1:
The invention extracts and utilizes the natural theta replication mechanism of circular DNA, removing the need for external primers and cyclization enzymes. By employing a primerless replication system with theta-type helicase and DNA polymerase, the method directly produces circular amplification products, eliminating the additional cyclization steps required by rolling circle amplification.
Solution Approach 2:
The circular DNA template serves its own replication initiation through the theta replication mechanism, where the helicase unwinds the DNA at the origin of replication and the polymerase synthesizes new strands using the circular template itself, without requiring externally added primers or subsequent cyclization enzymes.
2Quantity of substance
If conventional in vitro amplification methods are used, then amplification can be performed, but the DNA size is limited to within a few kbp and replication efficiency is low
Solution Approach 1:
The invention changes the fundamental parameters of the replication system by using theta-type helicase and DNA polymerase that are capable of handling long circular DNA molecules. This enzyme system allows replication of circular DNA exceeding 200 kb in size, dramatically expanding the amplifiable size range compared to conventional methods limited to a few kbp.
3Productivity
If cell-based DNA cloning is used to amplify circular DNA, then amplification can be achieved, but troublesome procedures such as cell cultivation and extraction/purification are required
Solution Approach 1:
The invention extracts the essential replication functions from living cells and implements them in a cell-free system. By using purified theta-type helicase, DNA polymerase, and other necessary components in an in vitro reaction mixture, the method achieves circular DNA amplification without requiring cell cultivation, transformation, or extraction procedures.
4Shape
If Escherichia coli minichromosome replication system is used, then circular amplification product can be produced, but template circular DNA cannot be amplified even to double
Solution Approach 1:
The invention creates an accurate copy of the circular DNA template through theta replication, where the helicase unwinds the circular DNA at the origin and the polymerase synthesizes complementary strands. This mechanism efficiently produces multiple circular copies from a single template, achieving amplification to double and beyond, unlike the minichromosome system.
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 enables easy and exponential amplification of circular DNA, including long chain DNA exceeding 200 kb, without the need for primers or cellular systems, and produces amplification products that maintain the circular structure of the original template.
Implementation Method 1
a first enzyme group that catalyzes replication of circular DNA
Implementation Method 2
a second enzyme group that catalyzes an Okazaki fragment maturation and synthesizes two sister circular DNAs constituting a catenane
Implementation Method 3
a third enzyme group that catalyzes a separation of two sister circular DNAs
Data Source
AI summary
Provided is a method capable of simply and exponentially amplifying circular DNA, and particularly, long-chain circular DNA, in a cell-free system. Specifically, provided herein is a method for amplifying circular DNA which comprises mixing circular DNA having a replication origin sequence (origin of chromosome (oriC)) with a reaction solution comprising: a first enzyme group that catalyzes replication of circular DNA; a second enzyme group that catalyzes an Okazaki fragment maturation and synthesizes two sister circular DNAs constituting a catenane; a third enzyme group that catalyzes a separation of two sister circular DNAs; and also, a buffer, NTP, dNTP, a magnesium ion source, and an alkali metal ion source, to form a reaction mixture, which is then reacted.