Abstract
DNA N6-methyladenine (6mA) is a potential epigenetic mark involved in gene transcription in eukaryotes, yet the regulatory mechanism governing its methyltransferase (MTase) activity remains obscure. Here, we exploited the 6mA MTase AMT1 to elucidate its auto-regulation in the unicellular eukaryote Tetrahymena thermophila. The detailed endogenous localization of AMT1 in vegetative and sexual stages revealed a correlation between the 6mA reestablishment in the new MAC and the occurrence of zygotically expressed AMT1. Catalytically inactive AMT1 reduced 6mA level on the AMT1 gene and its expression, suggesting that AMT1 modulated its own transcription via 6mA. Furthermore, AMT1-dependent 6mA regulated the transcription of its target genes, thereby affecting cell fitness. Our findings unveil a positive feedback loop of transcriptional activation on the AMT1 gene and highlight the crucial role of AMT1-dependent 6mA in gene transcription.