Two DNA-binding and nick recognition modules in human DNA ligase III

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Human DNA ligase III possesses an N-terminal zinc finger domain implicated in DNA nick sensing.
• This domain was previously thought to be non-essential for in vitro DNA nick joining activity.

Purpose of the Study:

• To investigate the DNA binding affinity and specificity of individual domains within human DNA ligase III.
• To elucidate the roles of different domains in DNA nick sensing and ligation.

Main Methods:

• Affinity and specificity measurements of DNA ligase III domains.
• Analysis of DNA binding using nicked and intact duplex DNA substrates.

Main Results:

• Identified two independent DNA-binding modules in DNA ligase III, both specific for nicked DNA.
• The zinc finger and DNA-binding domains function as a single unit, while the catalytic core is a separate binding module.
• Both modules are essential for ligating blunt-ended DNA substrates.

Conclusions:

• Human DNA ligase III possesses dual DNA nick-binding modules critical for its function.
• A jackknife model is proposed, suggesting conformational changes during nick sensing and ligation to enhance enzyme versatility.