ABSTRACT
Pseudouridylation is a prevalent post-transcriptional RNA modification that impacts many aspects of RNA biology and function. The conversion of uridine to pseudouridine (Ψ) is catalyzed by the family of pseudouridine synthases (PUSs). Development of robust methods to determine PUS-dependent regulation of Ψ location and stoichiometry in low abundant mRNA is essential for biological and functional understanding of pseudouridylation. Here, we present a framework, NanoPsiPy, for identifying Ψ sites and quantify their levels in poly-A RNA at single-nucleotide resolution using direct RNA long-read Nanopore sequencing, based on the observation that Ψ can cause characteristic U-to-C basecalling errors in Nanopore direct RNA sequencing data. Our method was able to detect low and high stoichiometric Ψ sites in human mRNA. We validated our method by transcriptome-wide quantitative profiling of PUS7-dependent Ψ sites in poly-A RNA from a MYCN -amplified neuroblastoma cell line. We identified 8,625 PUS7-dependent Ψ sites in 1,246 mRNAs that encode proteins involved primarily in ribosome biogenesis, translation, and mitochondrial energy metabolism. Our work provides the first example of using direct RNA long-read Nanopore sequencing for transcriptome-wide quantitative profiling of mRNA pseudouridylation regulated by a PUS. We envision that our method will facilitate functional interrogation of PUSs in biological and pathological processes.
