ABSTRACT
Ribonucleic acid (RNA) has long been known to contain modi ed nucleosides in addition to the four major bases. Modi ed nucleosides, which are present in all types of RNA, are particularly prevalent in tRNAs where there are 70 different nucleoside modi cations that only appear within these small RNAs. The different modi cations were originally summarized by Limbach et al.1 and a continuously updated database can be found at https://library.med.utah.edu/RNAmods/. Mass spectrometry (MS) is a valuable tool for their study because all modi ed nucleosides, with the exception of pseudouridine, result in a change in mass from the parent major nucleoside.
