Absolute quantification of single-base mA methylation in the mammalian transcriptome using GLORI.

N-methyladenosine (mA) is the most abundant RNA modification in mammalian cells and the best-studied epitranscriptomic mark. Despite the development of various tools to map mA, a transcriptome-wide method that enables absolute quantification of mA at single-base resolution is lacking. Here we use glyoxal and nitrite-mediated deamination of unmethylated adenosines (GLORI) to develop an absolute mA quantification method that is conceptually similar to bisulfite-sequencing-based quantification of DNA 5-methylcytosine. We apply GLORI to quantify the mA methylomes of mouse and human cells and reveal clustered mA modifications with differential distribution and stoichiometry. In addition, we characterize mA dynamics under stress and examine the quantitative landscape of mA modification in gene expression regulation. GLORI is an unbiased, convenient method for the absolute quantification of the mA methylome.