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Nicking by transesterification: the reaction catalysed by a relaxase
1Department of Biology, University of North Carolina at Chapel Hill, 27599, USA.
Molecular Microbiology
|November 14, 1997
Summary
DNA relaxases initiate and terminate conjugative DNA transfer by nicking DNA. This process involves a reversible transesterification reaction, forming a stable intermediate essential for DNA transfer between cells.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- DNA relaxases are key enzymes in conjugative DNA transfer.
- They facilitate DNA nicking and ligation during plasmid transfer.
- Relaxases form complexes with other proteins, known as relaxosomes.
Purpose of the Study:
- To elucidate the reaction mechanism of DNA relaxases.
- To understand the role of relaxases in conjugative DNA transfer initiation and termination.
- To characterize the covalent nucleoprotein intermediate formed during the reaction.
Main Methods:
- Purification and characterization of relaxases from various plasmids.
- Biochemical assays to study DNA nicking and ligation.
- Analysis of the covalent relaxase-DNA intermediate.
Main Results:
- Relaxases catalyze site- and strand-specific DNA nicking via transesterification.
- A covalent phosphotyrosyl linkage forms between the relaxase and the 5' DNA end.
- The reaction is reversible, with a second transesterification responsible for ligation.
- Some relaxases possess intrinsic DNA helicase activity for unwinding DNA.
Conclusions:
- DNA relaxases are crucial for both initiating and terminating conjugative DNA transfer.
- The stable covalent nucleoprotein complex is a vital intermediate in DNA transfer.
- Relaxase activity, coupled with DNA helicase function, ensures efficient DNA transfer to recipient cells.