Pseudouridine synthase-related <p>H/ACA ribonucleoprotein particles (RNPs) are a family of RNA pseudouridine synthases that specify modification sites through guide RNAs. More than 100 mammalian H/ACA RNAs form an equal number of ribonucleoproteins (RNPs) by associating with the same four core proteins: Cbf5, Gar1, Nhp2 and Nop10. The function of these H/ACA RNPs is essential for biogenesis of the ribosome, splicing of precursor mRNAs (pre-mRNAs), maintenance of telomeres and probably for additional cellular processes [<cite idref="PUB00053435"/>]. Recent crystal structures of archaeal H/ACA protein complexes show how the same four proteins accommodate &gt;100 distinct but related H/ACA RNAs [<cite idref="PUB00036066"/>]. The complex contains a stable core composed of Cbf5 and Nop10, to which Gar1 and Nhp2 subsequently bind, the complex interacts with snoRNAs [<cite idref="PUB00053436"/>].</p><p>This entry represents Cbf5, which plays a central role in ribosomal RNA processing. It is the catalytic subunit of H/ACA small nucleolar ribonucleoprotein (H/ACA snoRNP) complex, which catalyzes pseudouridylation of rRNA; point mutations in yeast Cbf5 abolish in vivo pseudouridylation of rRNA [<cite idref="PUB00053437"/>]. Pseudouridylation involves the isomerization of uridine such that the ribose is subsequently attached to C5, instead of the normal N1. Pseudouridine ('psi') residues may serve to stabilise the conformation of rRNAs. Cbf5 also binds in vitro to centromeres and microtubules. It is a centromeric DNA-Cbf3-binding factor which is also involved in mitotic chromosome segregation [<cite idref="PUB00053438"/>, <cite idref="PUB00053437"/>].</p>