H/ACA snoRNP structure highlighting the important interactions between H/ACA guide RNA and substrate RNA. Ribbon structure of an archaeal H/ACA snoRNP complex assembled on a single-hairpin H/ACA guide RNA with a short substrate RNA bound (PDB ID: 3HAY). The proteins are depicted and labeled in gray whereas the guide RNA is shown in blue to purple and the substrate RNA in red to yellow. The first two base-pairing interactions on either side of the target uridine are essential for pseudouridylation and are colored red and dark blue. The next two important base-pairing interactions are highlighted in orange and purple. The less important base pairs at the bottom of the pseudouridylation pocket are shown in yellow and pink.
