Selective retention of recombinant plasmids coding for human insulin.

Area of Science:

• Molecular Biology
• Genetics
• Biotechnology

Background:

• Plasmid instability is a significant challenge in Escherichia coli K-12 cultures, especially for chimeric plasmids used in recombinant DNA technology.
• Human insulin-coding plasmids derived from pBR322 are prone to loss without selective pressure.

Purpose of the Study:

• To engineer a system that ensures stable retention of chimeric plasmids in Escherichia coli K-12 hosts.
• To develop a method for preventing plasmid loss in the absence of selective markers.

Main Methods:

• Insertion of the cIts857 gene from bacteriophage lambda into the bla gene of human-insulin-coding plasmids (pIA7 delta 4 delta 1, pIB7 delta 4 delta 1, pHI7 delta 4 delta 1) to create new plasmids (pPR17, pPR18, pPR19).
• Expression of the cI gene from pM and pbla promoters.
• Lysogenization of E. coli K-12 RV308 host strains containing the new plasmids with repressor-defective bacteriophage lambda cI90.

Main Results:

• The engineered plasmids produced a thermosensitive lambda repressor.
• Loss of the plasmid from lysogens induced the lambda cI90 prophage into a lytic cycle, leading to cell death.
• This mechanism effectively enforced plasmid retention in all viable cells within the culture.

Conclusions:

• The developed system provides a robust method for stable plasmid maintenance in E. coli K-12.
• This approach overcomes the challenge of plasmid loss in non-selective culture conditions.
• The system has significant implications for biotechnological applications requiring stable expression of recombinant genes.