Pi Protein Switching for Screening-Tag-Free Plasmid Production

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Solution Overview

Problem

Existing gene therapy plasmids often carry antibiotic resistance genes that can cause antibiotic resistance in patients, necessitating the development of high-yield, high-purity antibiotic-resistance-tag-free plasmids to ensure safety and efficacy.

Innovation Solution

A method using a precursor plasmid with a conditioned replication initiation site, regulatory proteins, repressor proteins, and recombinase-mediated recombination to produce screening-tag-free plasmids, involving wild-type and mutant Π proteins to control plasmid replication and reduce bacterial sequences.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional plasmids carry antibiotic resistance genes for screening and stable inheritance, then cloning efficiency and stability are improved, but patient safety is compromised due to antibiotic resistance development

Engineering Contradiction:

Improveplasmid stabilityVSAvoidantibiotic resistance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent removes antibiotic resistance genes from the plasmid structure, extracting the harmful element while maintaining plasmid functionality through alternative screening mechanisms that do not rely on antibiotic resistance markers

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a conditional replication initiation site as an intermediary mechanism that controls plasmid replication through regulatory proteins, replacing the need for antibiotic resistance genes for plasmid maintenance and screening

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If antibiotic resistance genes are deleted to improve safety, then patient safety is improved, but plasmid yield and purity become difficult to control

Engineering Contradiction:

Improveantibiotic resistanceVSAvoidplasmid yield

Core Design Contradiction:

Object-affected harmful factorsVSProductivity

Solution Approach 1:

The patent changes the replication control parameters by introducing a conditional replication initiation site that responds to regulatory proteins, enabling precise control of plasmid copy number and replication timing to optimize yield without antibiotic markers

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements dynamic control of plasmid replication through regulatory proteins that can be induced or repressed, allowing the system to adapt plasmid replication rates based on cellular conditions for optimized yield

Inventive Principle:

Principle #15Dynamics

3Manufacturing precision

If antibiotic resistance genes are removed to reduce bacterial sequences, then plasmid purity is improved, but manufacturing complexity increases due to need for conditional replication control

Engineering Contradiction:

Improveplasmid purityVSAvoidreplication control system

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent makes the conditional replication initiation site serve multiple functions: it controls plasmid copy number, enables conditional replication, and works with regulatory proteins for both yield control and purity maintenance, reducing the need for separate control mechanisms

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

Enables large-scale production of antibiotic-free plasmids with reduced bacterial sequences, improving safety and stability for gene therapy applications.

Implementation Method 1

when bound to the expression regulatory sequence, the repressor protein inhibits the expression of the second regulatory protein

Methodology Applied

Scientific EffectTranscription inhibition:

Implementation Method 2

the paired recombination sites enable the self-recombination of the precursor plasmid in the presence of a recombinase to form a subplasmid and a circular double-stranded DNA

Methodology Applied

Scientific EffectRecombination:

Implementation Method 3

a conditioned replication initiation site having a plasmid replication initiation capacity that is dependent on regulatory proteins

Methodology Applied

Scientific EffectDNA replication:

Data Source

PatentUS20250354159A1Wild-type-mutant pi protein switching expression system capable of increasing efficiency of preparing screening-tag-free plasmid

Publication Date: 2025.11.20 NANJING GENSCRIPT BIOTECH CO LTD

AI summary

Provided is a precursor plasmid used for preparing a screening-tag-free plasmid, the precursor plasmid comprising: (1) a conditioned replication initiation site having a plasmid replication initiation capacity that is dependent on regulatory proteins, wherein the conditioned replication initiation site has a first replication initiation state in the presence of a first regulatory protein and a second replication initiation site in the presence of a second regulatory protein, and has a stronger ability to initiate plasmid replication in the second replication initiation state than in the first replication initiation state; 2) a first regulatory protein expression cassette expressing the first regulatory protein; 3) a sequence encoding a repressor protein; 4) a screened tag gene; 5) a target gene, or a cloning site for inserting the target gene; and 6) paired recombination sites. Also provided are a host cell suitable for the recombination of the precursor plasmid and the production of a screening-tag-free plasmid, and a method for large-scale production of the screening-tag-free plasmid.