Reduced background expression and improved plasmid stability with pET vectors in BL21 (DE3)

Area of Science:

• Molecular Biology
• Biotechnology
• Protein Expression

Background:

• The T7 polymerase-based pET System is a widely used prokaryotic expression system.
• Basal expression in BL21 (DE3) strains causes plasmid instability and variable yields, especially for toxic genes.
• High-stringency strains like BL21 (DE3) pLysS offer consistency but often reduce protein levels.

Purpose of the Study:

• To investigate catabolite repression as a method to control basal T7 polymerase expression in BL21 (DE3) strains.
• To achieve tight regulation and consistent expression comparable to BL21 (DE3) pLysS.
• To optimize protein yields by combining tight regulation with high expression levels.

Main Methods:

• Utilizing catabolite repression by switching to a poor carbon source during the final growth phases of BL21 (DE3) cultures.
• Monitoring basal expression levels of the T7 polymerase gene.
• Assessing plasmid stability and protein yields after induction.

Main Results:

• Catabolite repression effectively reduced basal T7 polymerase expression in BL21 (DE3).
• This method provided tight regulation and expression consistency similar to the BL21 (DE3) pLysS strain.
• Employing a poor carbon source in later growth stages allowed for high protein expression levels upon induction.

Conclusions:

• Catabolite repression is a viable strategy to enhance the performance of the BL21 (DE3) expression system.
• This approach offers a balance between tight regulation and high protein yield, overcoming limitations of existing methods.
• Optimizing carbon source utilization presents a simple yet effective means to improve prokaryotic protein expression.