Non-destructive enzymatic deamination enables single molecule long read sequencing for the determination of 5-methylcytosine and 5-hydroxymethylcytosine at single base resolution.
The predominant methodology for DNA methylation analysis relies on the chemical deamination by sodium bisulfite of unmodified cytosine to uracil to permit the differential readout of methylated cytosines. Bisulfite treatment damages the DNA leading to fragmentation and loss of long-range methylation information. To overcome this limitation of bisulfite treated DNA we applied a new enzymatic deamination approach, termed EM-seq (Enzymatic Methyl-seq) to long-range sequencing technologies. Our methodology, named LR-EM-seq (Long Range Enzymatic Methyl-seq) preserves the integrity of DNA allowing long-range methylation profiling of 5-mC and 5-hmC over several kilobases of genomic DNA. When applied to known differentially methylated regions (DMR), LR-EM-seq achieves phasing of over 5 kb resulting in broader and better defined DMRs compared to previously reported. This result demonstrated the importance of phasing methylation for biologically relevant questions and the applicability of LR-EM-seq for long range epigenetic analysis at single molecule and single nucleotide resolution.