Lambda Phage Plasmids for Homologous Recombination
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Solution Overview
Problem
Current methods for introducing homologous recombination functions into bacterial cells, such as E. coli and other gram-negative bacteria, are limited by the need for specific restriction sites and are laborious, especially when working with linear DNA fragments, which often degrade in bacteria and require special strains for transformation.
Innovation Solution
The use of mobilizable plasmids and lambda phages encoding recombination functions like Beta, Exo, and Gam, which allow for homologous recombination with short homology sequences (as short as 35 bases) without the need for restriction enzymes or DNA ligase, enabling efficient DNA manipulation in various bacterial species.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If restriction-ligation methods are used for DNA manipulation, then precise DNA combination is achieved, but the method is limited by availability of restriction sites and DNA fragment size
Solution Approach 1:
The patent changes the fundamental mechanism from restriction enzyme-based cutting and ligation to homologous recombination-based assembly. This parameter change allows DNA fragments of any size to be combined precisely using only homology sequences, eliminating the constraint of restriction site availability and enabling manipulation of large DNA molecules that were previously intractable
Solution Approach 2:
The patent replaces the mechanical restriction-ligation system with a biological homologous recombination system. Instead of using restriction enzymes that require specific recognition sequences and DNA ligase for joining, the system uses the cell's own homologous recombination machinery (RecA protein and associated factors) to assemble DNA fragments based on sequence homology, thereby eliminating the mechanical constraints of the original system
2Ease of operation
If linear DNA fragments are used for transformation, then short homology sequences suffice, but the DNA degrades in bacteria and requires special strains
Solution Approach 1:
The patent applies preliminary protective action by coating linear DNA fragments with single-stranded binding proteins (SSBs) before transformation. This preliminary step protects the DNA from degradation by bacterial exonucleases during the transformation process, allowing standard bacterial strains to be used without requiring special RecBCD- strains while maintaining high transformation efficiency
Solution Approach 2:
The patent introduces single-stranded binding proteins as intermediary protective agents between the linear DNA fragment and the bacterial degradation machinery. These SSBs bind to the DNA and prevent exonuclease access, serving as a protective intermediary that allows the DNA to survive long enough to undergo homologous recombination in standard bacterial strains
3Manufacturing precision
If recombineering functions are introduced using traditional methods, then homologous recombination is achieved, but the process is laborious and strain-specific
Solution Approach 1:
The patent creates a universal recombineering system using mobilizable plasmids that can transfer recombineering functions (Beta protein, Exo, and Gam) to any bacterial strain regardless of its native recombination capabilities. This universal system eliminates the need for strain-specific optimization and dramatically increases productivity by enabling efficient homologous recombination across diverse bacterial species with a single standardized protocol
Solution Approach 2:
The patent implements a self-service recombineering system where the mobilizable plasmid automatically transfers the necessary recombination functions (Beta, Exo, Gam) to the host cell during conjugation. The system is self-sufficient and does not require external intervention or strain-specific preparation, allowing researchers to simply introduce the plasmid and perform homologous recombination with short homology sequences in any bacterial strain
Data Source
AI summary
Lambda phages that can be used to introduce recombineering functions into host cells are disclosed. Also disclosed are plasmids that can be used to confer recombineering functions to a variety of strains of E. coli and to other bacteria, including Salmonella, Pseudomonas, Cyanobacteria, Spirochaetes. These plasmids and phages can be isolated in vitro and can be used to transform bacterial cells, such as gram negative bacteria.