StuI Restriction Endonuclease Expression in E. coli
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Solution Overview
Problem
The challenge lies in cloning and expressing the StuI restriction endonuclease and its accompanying methylase genes, as existing methods face hurdles such as unsuccessful methylase gene selection, low expression levels, and toxicity issues, making it difficult to produce recombinant StuI restriction endonuclease effectively in E. coli.
Innovation Solution
A strategy involving the use of non-cognate methylases like FnuDI to pre-modify the host DNA, combined with optimized cloning and expression techniques, such as incorporating StuI sites into the bla gene in pUC2iStuI and employing the Rosetta 2 strain for enhanced gene expression, is employed to overcome these challenges and achieve stable over-expression of the StuI restriction endonuclease.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the StuI restriction endonuclease and methylase genes are cloned and expressed in E. coli using conventional methods, then the production of recombinant StuI restriction endonuclease is attempted, but the expression levels are low and toxicity issues arise
Solution Approach 1:
The patent applies preliminary action by pre-modifying the host E. coli DNA with non-cognate methylases (such as FnuDI methylase) before introducing the StuI restriction endonuclease gene. This pre-modification protects the host DNA from cleavage by the StuI enzyme, preventing toxicity and enabling stable expression of the recombinant protein without self-destruction of the host genome.
Solution Approach 2:
The patent uses non-cognate methylases as intermediary enzymes that modify the host DNA to create protection against the StuI restriction endonuclease. These intermediary methylases act as mediators between the host DNA and the StuI enzyme, allowing the system to tolerate the presence of high levels of StuI restriction endonuclease without suffering from toxicity effects.
2Productivity
If the StuI restriction endonuclease gene is expressed at high levels, then productivity increases, but toxicity issues prevent stable expression
Solution Approach 1:
The patent applies preliminary anti-action by introducing non-cognate methylases that modify host DNA in advance, creating a protective effect against the toxic action of the StuI restriction endonuclease. This preliminary protective modification counteracts the harmful toxicity effect, enabling high-level expression without cell death or growth inhibition.
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 successfully yields high levels of recombinant StuI restriction endonuclease expression, with up to 5×10^6 units per gram of wet cells, and provides a stable expression system, overcoming previous obstacles in cloning and expression.
Implementation Method 1
Methyltransferases bind to the same sequences in dsDNA as the restriction endonucleases they accompany, but instead of cleaving the DNA, they alter it by the addition of a methyl group to one of the bases within the sequence. This methylation ('modification') prevents the restriction endonuclease from binding to the cleavage sequence, rendering the site resistant to cleavage.
Implementation Method 2
Restriction endonucleases bind to specific sequences of nucleotides ('recognition sequence') in double-stranded DNA molecules (dsDNA) and cleave the DNA, usually within or close to the sequence, generating DNA fragments of various sizes.
Data Source
AI summary
The present invention relates to compositions including: (1) isolated DNA encoding the StuI restriction endonuclease and isolated DNA encoding cognate and non-cognate methylase; (2) vectors and cells containing the isolated DNA; and (3) methods for producing the StuI restriction endonuclease.