Catalytic subunit of H/ACA small nucleolar ribonucleoprotein (H/ACA snoRNP) complex, which catalyzes pseudouridylation of rRNA (PubMed:10523634, PubMed:9315678, PubMed:9472021, PubMed:9848653). This involves the isomerization of uridine such that the ribose is subsequently attached to C5, instead of the normal N1 (PubMed:10523634, PubMed:9315678, PubMed:9472021, PubMed:9848653). Pseudouridine ('psi') residues may serve to stabilize the conformation of rRNAs and play a central role in ribosomal RNA processing (PubMed:10523634, PubMed:9315678, PubMed:9472021, PubMed:9848653). The H/ACA snoRNP complex also mediates pseudouridylation of other types of RNAs (PubMed:21131909, PubMed:25219674). Catalyzes pseudouridylation at position 93 in U2 snRNA (PubMed:21131909). Also catalyzes pseudouridylation of mRNAs; H/ACA-type snoRNAs probably guide pseudouridylation of mRNAs (PubMed:25219674). It is a centromeric DNA-CBF3-binding factor which is involved in mitotic chromosome segregation (PubMed:8336724). Essential for cell growth (PubMed:8336724). uridine in 5S rRNA = pseudouridine in 5S rRNA uridine in snRNA = pseudouridine in snRNA a uridine in mRNA = a pseudouridine in mRNA Component of the small nucleolar ribonucleoprotein particles containing H/ACA-type snoRNAs (H/ACA snoRNPs) (PubMed:9472021, PubMed:9848653, PubMed:15388873, PubMed:21131909). The protein component of the H/ACA snoRNP contains CBF5, GAR1, NHP2 and NOP10 (PubMed:9472021, PubMed:9848653, PubMed:15388873). The complex contains a stable core composed of CBF5 and NOP10, to which GAR1 and NHP2 subsequently bind (PubMed:9472021, PubMed:9848653, PubMed:15388873). Also interacts with NAF1 and SHQ1, which may be required for assembly of H/ACA snoRNP complexes. May also associate with the CBF3 110 kDa subunit (CBF2). Interacts with the trimethylguanosine synthase (TGS1) and with NOP53. Present with 33600 molecules/cell in log phase SD medium. Belongs to the pseudouridine synthase TruB family.