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Cloning the KpnI restriction-modification system in Escherichia coli
A W Hammond1, G F Gerard, D K Chatterjee
1Life Technologies, Incorporated, Bethesda Research Laboratories, Gaithersburg, MD 20877.
Gene
|January 2, 1991
Summary
Researchers successfully cloned and expressed the KpnI restriction and modification system genes from Klebsiella pneumoniae in E. coli. This engineered E. coli strain produces significantly higher yields of the KpnI restriction enzyme (R.KpnI).
Area of Science:
- Molecular Biology
- Genetics
- Biotechnology
Background:
- The KpnI restriction and modification (R-M) system from Klebsiella pneumoniae recognizes the DNA sequence 5'-GGTAC C-3'.
- Cloning and expression of R-M systems in heterologous hosts are crucial for producing enzymes for molecular biology applications.
- Challenges exist in co-expressing restriction endonuclease (ENase) and methyltransferase (MTase) genes due to potential toxicity or instability.
Purpose of the Study:
- To clone and express the KpnI R-M system genes (kpnIR and kpnIM) from K. pneumoniae in Escherichia coli.
- To develop a high-yield production system for the KpnI restriction enzyme (R.KpnI).
- To overcome challenges in co-expressing the ENase and MTase genes.
Main Methods:
- Cloning of kpnIR and kpnIM genes into E. coli expression vectors.
- Utilizing compatible plasmids for co-expression of ENase and MTase genes.
- Employing a strategy of initial MTase expression for host protection before introducing the ENase gene.
- Generating a chromosomal map to localize the kpnIR and kpnIM genes.
- Constructing a final E. coli strain (AH29) with inducible expression of kpnIR and constitutive expression of M.KpnI.
Main Results:
- Successful cloning and co-expression of kpnIR and kpnIM genes in E. coli.
- Development of a stable E. coli strain (AH29) capable of high-level R.KpnI production.
- Achieved production of approximately 10 million units of R.KpnI per gram of wet-weight cells, a several thousand-fold increase compared to K. pneumoniae.
- Demonstrated that DNA methylated by M.KpnI in vivo is not restricted by E. coli's mcrA, mcrB, or mrr systems.
Conclusions:
- The KpnI R-M system can be efficiently expressed in E. coli using a carefully designed cloning and expression strategy.
- The engineered E. coli strain AH29 is a highly productive source of R.KpnI enzyme.
- This work provides a valuable tool for molecular biology applications requiring the KpnI restriction enzyme.