How M.MspI and M.HpaII decide which base to methylate

Area of Science:

• Molecular Biology
• Enzymology
• DNA Methylation

Background:

• HpaII methylase (M.HpaII) and MspI methylase (MspI) recognize the CCGG sequence.
• M.HpaII methylates the inner cytosine, while MspI methylates the outer cytosine.
• Both enzymes share conserved motifs but differ in their variable regions responsible for sequence recognition.

Purpose of the Study:

• To investigate the role of the variable region in determining methylation specificity.
• To construct and analyze hybrids of M.HpaII and MspI methylases.

Main Methods:

• Construction of chimeric DNA methylase enzymes.
• Analysis of methylation properties of wild-type and hybrid methylases.

Main Results:

• A hybrid with the variable region from MspI methylated the outer cytosine.
• A hybrid with the variable region from M.HpaII methylated the inner cytosine.
• The variable region dictates the specific base methylated within the CCGG sequence.

Conclusions:

• The variable region of DNA methyltransferases is the primary determinant of methylation site specificity.
• Understanding this mechanism is crucial for DNA epigenetics and enzyme engineering.