Micro-flow hydrophilic interaction liquid chromatography coupled with triple quadrupole mass spectrometry detects modified nucleosides in the transfer RNA pool of cyanobacteria.

Post-transcriptional modification of nucleosides is observed in almost all elements of RNA. Modified nucleosides finely tune the structure of RNA molecules and affect vital functions, such as the modified wobble position 34 of transfer RNAs expanding the reading preference of anticodons to codons. Recent investigations have revealed that the modification species and their frequencies in an RNA element are not stable but vary with specific cellular factors including metabolites and particular proteins (writers, readers, and erasers). To understand the link between dynamic RNA modifications and biological processes, sensitive and reliable methods for determining modified nucleosides are required. In this study, micro-flow (8 μL/min) hydrophilic interaction liquid chromatography was coupled with triple quadrupole mass spectrometry for the simultaneous determination of adenosine, uridine, cytidine, guanosine, and 20 modified nucleosides. The method was calibrated using 0.1-1000 nM standards (∼0.03-300 ng/mL) and successfully applied to the determination of transfer RNA modifications in the model cyanobacterium Synechococcus elongatus PCC 7942. A protocol for the isolation of a clean transfer RNA pool was optimized, requiring only 25 ng for the identification and quantification of transfer RNA modifications. This micro-flow liquid chromatography-tandem mass spectrometry method constitutes the first step toward monitoring dynamic ribonucleoside modifications in a limited RNA sample.