Transmission of DNA N6-adenine methylation (6mA) in Tetrahymena thermophila

DNA N6-adenine methylation (6mA) is best known in prokaryotes, its presence in eukaryotes has lately been extensively investigated. Biochemical and genetic evidence supports that AMT1, a MT-A70 family methyltransferase (MTase), is crucial for 6mA deposition in unicellular eukaryotes6,7. Nonetheless, its transmission mechanism and function remain to be elucidated. Taking advantage of single molecule long-read sequencing8, here we provide definitive evidence for semi-conservative transmission of 6mA in the ciliate Tetrahymena thermophila. Our study dissects AMT1-dependent maintenance methylation and AMT1-independent de novo methylation, reveals a molecular pathway for 6mA transmission with striking similarity to 5-methyl cytosine (5mC) transmission at the CpG dinucleotide, and establishes 6mA as a bona fide transcription-associated epigenetic mark in eukaryotes.