DNA topoisomerase I from Diplococcus pneumoniae

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Topoisomerases are essential enzymes that manage DNA topology.
• Type I topoisomerases play a crucial role in DNA replication and transcription.
• Understanding their specific activities and substrate preferences is key to deciphering DNA metabolism.

Purpose of the Study:

• To purify and characterize a type I topoisomerase from Diplococcus pneumoniae.
• To investigate the enzyme's catalytic activities, including DNA relaxation.
• To determine the influence of DNA methylation on the enzyme's function.

Main Methods:

• Purification of type I topoisomerase using phosphocellulose and hydroxylapatite chromatography.
• Assay of DNA relaxation activity using supercoiled DNA substrates.
• Analysis of enzyme activity on plasmids with varying methylation states (dam and dcm).

Main Results:

• A functional type I topoisomerase was successfully purified from Diplococcus pneumoniae.
• The enzyme specifically catalyzes the relaxation of negatively supercoiled DNA.
• Enzyme activity requires Mg2+ and is enhanced by monovalent cations.
• No catenating or supercoiling activities were observed.
• DNA relaxation showed slightly higher efficiency on plasmids with methylated adenine in GATC sequences (dam+), but no difference was observed for dcm methylation.

Conclusions:

• The purified Diplococcus pneumoniae type I topoisomerase is a DNA relaxing enzyme.
• Enzyme activity is dependent on divalent cations and influenced by monovalent cations.
• DNA methylation at GATC sites (dam methylation) can affect the enzyme's relaxation efficiency, suggesting a role in DNA processing.
• The enzyme does not appear to be affected by dcm methylation.