A facile and reversible method to decrease the copy number of the ColE1-related cloning vectors commonly used in...

Area of Science:

• Molecular Biology
• Genetics
• Biotechnology

Background:

• ColE1-type plasmids are widely used but their high copy number can complicate gene expression studies.
• Transposon Tn1000 mediates DNA integration through a two-step process involving cointegrate formation and resolution.

Purpose of the Study:

• To develop a method for reducing the copy number of ColE1-type plasmids.
• To create stable, low-copy plasmids for studying gene expression.
• To investigate the effect of plasmid copy number on fabA gene expression.

Main Methods:

• Engineered Tn1000 transposon to block resolution step, forcing stable cointegrate formation.
• Constructed cointegrate plasmids between an F factor and a ColE1-type plasmid.
• Utilized a polA strain for stable maintenance of cointegrates.
• Assayed chloramphenicol acetyltransferase expression to determine plasmid copy number.

Main Results:

• Successfully created stable F factor-ColE1 cointegrate plasmids with significantly reduced copy numbers.
• Demonstrated that replication from the ColE1 origin was inhibited, with replication dependent on the single-copy F factor origin.
• Achieved copy numbers comparable to single-copy chromosomal elements.
• Used the low-copy plasmids to study the copy number-dependent expression of the fabA gene regulated by FadR.

Conclusions:

• The engineered Tn1000 transposition system provides a robust method for generating stable, low-copy plasmids.
• This technique is valuable for studying genes where high plasmid copy numbers interfere with normal regulation.
• The method facilitates the analysis of gene expression under controlled, reduced copy number conditions.