Identification, expression, and purification of DNA cytosine 5-methyltransferases with short recognition sequences

Background: DNA methyltransferases (MTases) are enzymes that induce methylation, one of the representative epigenetic modifications of DNA, and are also useful tools for analyzing epigenomes. However, regarding DNA cytosine 5-methylation, MTases identified so far have drawbacks in that their recognition sequences overlap with those for intrinsic DNA methylation in mammalian cells and/or that the recognition sequence is too long for fine epigenetic mapping. To identify MTases with short recognition sequences that never overlap with the CG dinucleotide, we systematically investigated the 25 candidate enzymes identified using a database search, which showed high similarity to known cytosine 5-MTases recognizing short sequences. Results: We identified MTases with six new recognition sequences, including TCTG, CC, CNG, TCG, GCY, and GGCA. Because the recognition sequence never overlapped with the CG dinucleotide, MTases recognizing the CC dinucleotide were promising. Conclusions: In the current study, we established a procedure for producing active CC-methylating MTases and applied it to nucleosome occupancy and methylome sequencing to prove the usefulness of the enzyme for fine epigenetic mapping. MTases that never overlap with CG dinucleotides would allow us to profile multiple epigenomes simultaneously.