Practice question

Box H/ACA small nucleolar RNAs contain two hairpin structures linked by H box ANANNA and terminated by ACA box three nucleotides from three prime end, forming hairpin-hinge-hairpin-tail architecture. Each hairpin harbors internal pseudouridylation pocket with antisense elements flanking target uridine left unpaired for isomerization. Core proteins include pseudouridine synthase dyskerin Cbf5, NOP10, Nhp2, Gar1. Dyskerin isomerizes uridine to pseudouridine via base rotation adding extra NH hydrogen donor strengthening base stacking and water-mediated interactions, enhancing ribosome stability. Mutations cause dyskeratosis congenita with bone marrow failure and ribosome biogenesis defects.