Common analysis of direct RNA sequencinG CUrrently leads to misidentification of m5C at GCU motifs

Abstract

RNA modifications, such as methylation, can be detected with Oxford Nanopore Technologies direct RNA sequencing. One commonly used tool for detecting 5-methylcytosine (m⁵C) modifications is Tombo, which uses an "Alternative Model" to detect putative modifications from a single sample. We examined direct RNA sequencing data from diverse taxa including viruses, bacteria, fungi, and animals. The algorithm consistently identified a m⁵C at the central position of a GCU motif. However, it also identified a m⁵C in the same motif in fully unmodified in vitro transcribed RNA, suggesting that this is a frequent false prediction. In the absence of further validation, several published predictions of m⁵C in a GCU context should be reconsidered, including those from human coronavirus and human cerebral organoid samples.