The function of PUS1 (pseudouridine synthase 1, ENSG00000177192) is as follows. Pseudouridylate synthase that catalyzes pseudouridylation of tRNAs and mRNAs (PubMed:15772074, PubMed:24722331). Acts on positions 27/28 in the anticodon stem and also positions 34 and 36 in the anticodon of an intron containing tRNA (PubMed:24722331). Also catalyzes pseudouridylation of mRNAs: mediates pseudouridylation of mRNAs with the consensus sequence 5'-UGUAG-3' (PubMed:31477916, PubMed:35051350). Acts as a regulator of pre-mRNA splicing by mediating pseudouridylation of pre-mRNAs at locations associated with alternatively spliced regions (PubMed:35051350). Pseudouridylation of pre-mRNAs near splice sites directly regulates mRNA splicing and mRNA 3'-end processing (PubMed:35051350). Involved in regulation of nuclear receptor activity through pseudouridylation of SRA1 mRNA (PubMed:24722331). {ECO:0000269|PubMed:15772074, ECO:0000269|PubMed:24722331, ECO:0000269|PubMed:31477916, ECO:0000269|PubMed:35051350}.