Figure 5.

Constitutive and induced pseudouridylation by snR81 box H/ACA ribonucleoprotein. The sequence and structure of snR81 box H/ACA RNA is shown. As arrows indicate, the internal loop (pseudouridylation pocket) within the 5’ hairpin is specific for Ψ42 (constitutive) of U2 snRNA, and the internal loop within the 3’ hairpin is specific for Ψ1051 (constitutive) of 25S rRNA. Under stress coditions, the 3’ pseudouridylation pocket becomes capable of directing the formation of Ψ93 (inducible) of U2 snRNA. As shown by “x”, there are two U-U mismatches between the 3’ pocket and the U2 sequence flanking position 93.