Quantitative analysis of small RNA pseudouridylation reveals interplay of PUS enzymes in tRNA anticodon stem-loop

Pseudouridine (Ψ) is an abundant modification in small RNA catalyzed by multiple pseudouridine synthases (PUSs). However, the substrate specificity of human PUSs remains elusive. Here, we adopted PRAISE, a quantitative Ψ detection method, to profile pseudouridylation in small RNA, including cytosolic and mitochondrial tRNAs, snRNA, and snoRNA. We found that snoRNA pseudouridylation is mediated not only by RNA-guided DKC1, but also by the stand-alone enzyme PUS7 at a specific site. Interestingly, several PUS enzymes, including PUS1, RPUSD1, and PUS7, which install nearby Ψ sites within tRNA anticodon stem-loop, can influence pseudouridylation catalyzed by other PUSs, revealing an unrecognized interplay during Ψ formation. For the three RluA family enzymes, RPUSD1 catalyzes the canonical Ψ30 in tRNA-Ile and Ψ72 in tRNA-Arg isoacceptors. RPUSD2 pseudouridylates Ψ31 of mt-tRNA^Leu(CUN), Ψ32 of mt-tRNA^Pro and mt-tRNA^Cys, whereas RPUSD3 lacks tRNA activity. Together, our quantitative Ψ profiling characterized PUS tRNA substrates and revealed unexpected PUS interplay.