CpG underrepresentation and the bacterial CpG-specific DNA methyltransferase M.MpeI

Area of Science:

• Molecular Biology
• Genomics
• Biochemistry

Background:

• Cytosine methylation is linked to deamination and CpG underrepresentation in eukaryotic genomes.
• The diagnostic role of CpG scarcity in prokaryotic genomes concerning methylation remains unclear.

Purpose of the Study:

• To investigate the relationship between CpG depletion and DNA methylation in prokaryotes, specifically Mycoplasms.
• To characterize the CpG-specific DNA methyltransferase M.MpeI from Mycoplasma penetrans.

Main Methods:

• Genome-wide sequencing of bisulfite-converted DNA.
• In vitro and in vivo methylation assays.
• X-ray crystallography of M.MpeI with DNA.

Main Results:

• Mycoplasms exhibit CpG depletion and possess CpG-specific DNA methyltransferases.
• M.MpeI methylates CpG sites in a locus-nonselective manner both in vivo and in vitro.
• Crystal structure reveals base flipping and specific interactions within the CpG site, similar to eukaryotic methyltransferases.

Conclusions:

• CpG scarcity in Mycoplasma genomes is associated with the presence of CpG-specific DNA methyltransferases.
• M.MpeI shares mechanistic features with eukaryotic DNA methyltransferases in recognizing and methylating CpG sites.
• This study provides insights into the evolution and function of DNA methylation in prokaryotes.