Pseudouridine synthase PusS from?Escherichia coli?specifically acts on uridine13?in tRNA [2,3]. The Pus7 protein from?Saccharomyces cerevisiae?is a multisite-multisubstrate pseudouridine synthase that is able to modify uridine13?in several yeast tRNAs, uridine35?in the pre-tRNATyr, uridine35?in U2 small nuclear RNA, and uridine50?in 5S rRNA [5].