Reversible RNA Modification N1-methyladenosine (m1A) in mRNA and tRNA

More than 100 modifications have been found in RNA. Analogous to epigenetic DNA methylation, epitranscriptomic modifications can be written, read, and erased by a complex network of proteins. Apart from N6-methyladenosine (m6A), N1-methyladenosine (m1A) has been found as a reversible modification in tRNA and mRNA. m1A occurs at positions 9, 14, and 58 of tRNA, with m1A58 being critical for tRNA stability. Other than the hundreds of m1A sites in mRNA and long non-coding RNA transcripts, transcriptome-wide mapping of m1A also identifies >20 m1A sites in mitochondrial genes. m1A in the coding region of mitochondrial transcripts can inhibit the translation of the corresponding proteins. In this review, we summarize the current understanding of m1A in mRNA and tRNA, covering high-throughput sequencing methods developed for m1A methylome, m1A-related enzymes (writers and erasers), as well as its functions in mRNA and tRNA.