DNA recognition by the EcoP15I and EcoPI modification methyltransferases

Area of Science:

• Molecular Biology
• Enzymology
• DNA Methylation

Background:

• Type-III restriction-modification enzymes, including EcoP15I DNA methyltransferase (M.EcoP15I), play crucial roles in DNA metabolism.
• Understanding the DNA-binding properties of M.EcoP15I is essential for elucidating its enzymatic mechanism and biological function.

Purpose of the Study:

• To investigate the DNA-binding characteristics of M.EcoP15I.
• To determine the oligomeric state of M.EcoP15I in solution.
• To explore the influence of ATP and S-adenosylmethionine (AdoMet) on sequence-specific DNA recognition by M.EcoP15I.

Main Methods:

• Electrophoretic mobility shift assays (EMSAs) were employed to study DNA-protein interactions.
• Molecular size-exclusion chromatography and dimethyl suberimidate cross-linking were used to determine the enzyme's quaternary structure.

Main Results:

• M.EcoP15I exists as a dimer in solution.
• ATP significantly enhances the discrimination between specific (5'-CAGCAG-3') and non-specific DNA sequences compared to AdoMet alone.
• Mutant M.EcoP15I enzymes, defective in AdoMet binding, retain sequence-specific DNA binding capabilities.

Conclusions:

• ATP plays a novel role in modulating DNA recognition by type-III restriction-modification enzymes.
• The dimeric nature of M.EcoP15I is important for its DNA-binding activity.
• Sequence-specific DNA binding by M.EcoP15I can occur independently of AdoMet binding in certain mutant forms.