P1 plasmid replication. Purification and DNA-binding activity of the replication protein RepA

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• The P1 replicon requires the essential replication protein RepA for its function.
• RepA interacts with repeated DNA sequences, incA and incC, within the P1 replicon.
• incA repeats are implicated in controlling plasmid copy number, while incC repeats are part of the origin of replication and contain the repA promoter.

Purpose of the Study:

• To investigate the specific binding interaction between the P1 replication protein RepA and the incA and incC repeated DNA sequences.
• To understand the role of RepA-repeat interactions in regulating P1 replication and RepA synthesis.

Main Methods:

• Overproduction and purification of the RepA protein to 90% homogeneity.
• Electrophoretic mobility shift assays (EMSAs) were used to detect and characterize RepA-DNA complex formation.
• Assays monitored the binding of purified RepA to DNA fragments containing incA and incC repeat sequences.

Main Results:

• Purified RepA specifically bound to DNA fragments containing the incA and incC repeat sequences.
• The number of retarded bands observed in EMSAs correlated with the number of repeat units in the DNA fragment.
• No RepA binding was detected with DNA fragments lacking these specific repeat sequences.

Conclusions:

• RepA exhibits specific DNA-binding activity directed towards the incA and incC repeat sequences within the P1 replicon.
• This specific binding is likely fundamental to RepA's diverse roles, including origin function, autoregulation, and copy number control.
• The findings suggest a direct mechanism by which RepA mediates its regulatory functions through sequence-specific DNA interactions.