WITHDRAWN: Detection of N3-methylcytidine in RNA at single base resolution using Protoscript II to read through and generate high mutation rates

Abstract

N3-methylcytidine (m3C), an RNA modification involving methylation of cytidine at the Watson-Crick face, has been identified in human tRNA, mitochondrial tRNA (mt-tRNA), and mRNA. In tRNA and mt-tRNA, it has been shown to play important roles in tRNA structure and translation. m3C remains understudied in mRNA and other low-abundance RNAs due to its markedly lower levels, the lack of high-resolution techniques to reproducibly map its location, and under-characterization of its effector proteins on these RNA types. Here we describe a new approach which utilizes the high readthrough and mutation rates of Protoscript II (PSII) at m3C sites in combination with AlkB demethylation to detect m3C at single-base resolution. We first validate the method on synthetic probes. Then, using this method, we successfully identify the known m3C sites on tRNA and mt-tRNA and show that none of the m3C sites identified in cytosolic tRNA are likely METTL8 substrates. In contrast, the two m3C sites detected in mt-tRNA are installed by METTL8 since they are sensitive to METTL8 knockdown (KD) and over expression (OE). These results demonstrate that the method can be used to investigate changes in the m3C level in many sites using an unbiased approach. Overall, this study introduces a convenient high-resolution method for m3C mapping with high readthrough rates, paving the way for future mechanistic studies on the biological function of m3C and its effector proteins.