Studies on nuclease alpha from Ustilago maydis

Area of Science:

• Molecular Biology
• Enzymology
• Biochemistry

Background:

• Single-stranded DNA-specific endonucleases play crucial roles in DNA repair and recombination.
• Understanding the properties and substrate specificity of these enzymes is vital for elucidating DNA metabolism pathways.

Purpose of the Study:

• To extensively purify and characterize a novel endonuclease from Ustilago maydis.
• To investigate the enzyme's activity on various DNA substrates, including damaged and mismatched DNA.

Main Methods:

• Purification of the endonuclease from Ustilago maydis.
• Biochemical assays to determine enzyme activity, cofactor requirements, and inhibition patterns.
• Substrate specificity analysis using superhelical, relaxed circular, heteroduplex, and linear DNA molecules with specific lesions.

Main Results:

• The purified enzyme is a 55,000-dalton polypeptide, active on single-stranded DNA.
• Enzyme activity is stimulated by Co2+, Mn2+, and Zn2+ and inhibited by EDTA and 2-mercaptoethanol.
• The enzyme efficiently cleaves DNA at depurinated, deaminated, or radiation-damaged sites in heteroduplex DNA but not at single mismatched base pairs without additional distortion.
• Superhelical DNA is converted to open circular and then linear forms, while relaxed closed circular duplex DNA is resistant.
• Linear duplex DNA is digested from both 5' and 3' termini.

Conclusions:

• The Ustilago maydis endonuclease exhibits specificity for single-stranded DNA and preferentially cleaves damaged DNA sites.
• This enzyme likely plays a significant role in DNA repair mechanisms within Ustilago maydis.
• Further studies are warranted to explore its precise in vivo function and potential applications.