Box H/ACA ribonucleoproteins (RNPs), each consisting of one unique guide RNA and 4 common core proteins, constitute a family of complex enzymes that catalyze, in an RNA-guided manner, the isomerization of uridines to pseudouridines (Ψs) in RNAs, a reaction known as pseudouridylation. Over the years, box H/ACA RNPs have been extensively studied revealing many important aspects of these RNA modifying machines. In this review, we focus on the composition, structure, and biogenesis of H/ACA RNPs. We explain the mechanism of how this enzyme family recognizes and specifies its target uridine in a substrate RNA. We discuss the substrates of box H/ACA RNPs, focusing on rRNA (rRNA) and spliceosomal small nuclear RNA (snRNA). We describe the modification product Ψ and its contribution to RNA function. Finally, we consider possible mechanisms of the bone marrow failure syndrome dyskeratosis congenita and of prostate and other cancers linked to mutations in H/ACA RNPs.
Keywords: DC, dyskeratosis congenita; H/ACA; HH, hoyeraal-hreidarsson syndrome; PIKK, phosphatidylinositol 3-kinase-related kinase; PUA, pseudouridylase and archaeosine transglycosylase; RNA modification; RNA-guided; RNP, ribonucleoprotein; SMN, survival of motor neuron protein; SSD, SHQ1 specific domain; U, uridine; X-DC, X-linked dyskeratosis congenita; dyskeratosis congenita; prostate cancer; pseudouridine; rRNA; rRNA, ribosomal RNA; ribonucleoproteins; sca, small Cajal body; snRNA, small nuclear RNA; sno, small nucleolar; snoRNA; snoRNA, small nucleolar RNA; spliceosomal small nuclear RNA; tRNA, transfer RNA; ψ, pseudouridine, 5-ribosyluracil.