impossible. Here, we aim to add to the importance of this seminal report with additional insights into where the field of RNA modification research intersects that of infection biology. We provide a more elaborate description of key references and posit just a few ways that the success of the proposed path from the NASEM report could change the way we consider infectious diseases. We encourage the readers of this perspective to also visit the NASEM report to better appreciate the entire landscape of RNA modifications research, through the lens of many of the very researchers that made seminal discoveries to establish the field.■ WHAT IS AN RNA MODIFICATION AND HOW DO WE MAP THEM?RNA is decorated with over 170 known chemical modifications that influence RNA function, stability, structure, and interaction with other macromolecules including nucleic acids and proteins. These chemical modifications range from small alterations like methylations and acetylations to bulky modifications like those of glutamyl-queuosine (GluQ) or 5c a r b o x y m e t h y l a m i n o m e t h y l -2 -g e r a n y l t h i o u r i d i n e (cmnm 5 ges 2 U). 2 Sometimes these modifications appear to be permanent additions to the RNA, whereas in other cases, modifications like N 6 -methyladenosine (m 6 A) or 4-thiouridine (s4U) are reversible and highly regulated. 3,4 Importantly, a single RNA molecule can harbor multiple modifications, resulting in numerous structures and functionalities. The implication here is that one gene (DNA sequence) can encode for myriad variations of mature RNA molecules based on these chemical decorations, the collection of which is termed the epitranscriptome. It is now appreciated that there is not one epitranscriptome as there is one genome, but instead a collection of epitranscriptomes depending on the cell type, environmental growth conditions, lifecycle stage, etc. 1 tRNAs harbor the largest number of modifications in both prokaryotes and eukaryotes with roughly 14 per molecule on average; 5 however, rRNA also require abundant modification for proper function. In eukaryotes, modifications are also regularly observed on mRNA and noncoding RNAs, whereas these modifications appear to be less common on the nonstructural prokaryotic RNAs. 5 We definitely have a long way to go to completely understand all of the RNA modifications within even the simplest of organisms, but the NASEM report encourages the first steps toward defining a single epitranscriptome in full and the long-term goal of being able to even assess more complex and dynamic epitranscriptomes.RNA modifications can currently be incompletely mapped using a variety of techniques, including mass spectrometry, next-generation RNA-sequencing technologies, and the emerging direct RNA sequencing approaches like the Oxford Nanopore Technologies (ONT) sequencing platform, among many others (Figure 1). 6 Each of these techniques has strengths and weaknesses, but none are presently able to sequence all RNA modifications on a single RNA to determine the full epitran...
