No abstract

In this report, we perform structure validation of recently reported RNA phosphorothioate (PT) modifications, a new set of epitranscriptome marks found in bacteria and eukaryotes including humans. By comparing synthetic PT‐containing diribonucleotides with native species in RNA hydrolysates by high‐resolution mass spectrometry (MS), metabolic stable isotope labeling, and PT‐specific iodine‐desulfurization, we disprove the existence of PTs in RNA from E. coli, S. cerevisiae, human cell lines, and mouse brain. Furthermore, we discuss how an MS artifact led to the initial misidentification of 2′‐O‐methylated diribonucleotides as RNA phosphorothioates. To aid structure validation of new nucleic acid modifications, we present a detailed guideline for MS analysis of RNA hydrolysates, emphasizing how the chosen RNA hydrolysis protocol can be a decisive factor in discovering and quantifying RNA modifications in biological samples.

Recent advances in peroxidase-mediated biotin tyramide (BT) signal amplification technology have resulted in high-resolution and subcellular compartment-specific mapping of protein and RNA localization. Horseradish peroxidase (HRP) in the presence of H 2 O 2 is known to activate phenolic compounds for phenoxy radical reaction with nucleic acids, where biotinylation by BT is a practical example. BT reactivity with RNA and DNA is not understood in detail. We report that BT phenoxy radicals react in a sequence-independent manner with guanosine bases in RNA. In contrast, DNA reactivity with BT cannot be detected by our methods under the same conditions. Remarkably, we show that fluorescein conjugates DNA rapidly and selectively reacts with BT phenoxy radicals, allowing convenient and practical biotinylation of DNA on fluorescein with retention of fluorescence.