SRA

Chemical modifications on mRNA are increasingly recognized as a critical regulatory layer of the flow of genetic information, but quantitative tools to monitor RNA modifications in a whole-transcriptome and site-specific manner are lacking. Here we describe a versatile directed evolution platform that rapidly selects for reverse transcriptases that install mutations during reverse transcription at sites of a given type of RNA modification, allowing for site-specific identification of the modification. To develop and validate the platform, we evolved the HIV-1 reverse transcriptase against N1-methyladenosine (m1A). Iterative rounds of selection yielded reverse transcriptases with both robust read-through and high mutation rates at m1A sites. We apply the evolved reverse transcriptase to identify thousands of statistically confident m1A sites in human mRNA, some of which can be detected in antibody-free RNA-seq libraries. Together, this work develops and validates the reverse transcriptase evolution platform and provides new tools, analysis methods, and datasets to study m1A biology. Overall design: m1A-IP-seq and m1A-quant-seq experiments were performed on mRNA extracted from HEK-293T cells with three biological replicates.