Figure 7.

Simplified model depicting the observed conformational changes in the guide RNA and RNA–protein interactions in sub-complexes of the H/ACA RNP. Our footprinting data suggest that the upper stem of the guide RNA is not stably formed in the absence of L7Ae (A and B). Binding of L7Ae at the k-turn induces formation of the upper stem and establishes the pseudouridylation pocket (C). Cbf5 interacts with box ACA, the lower stem, the pseudouridylation pocket, and a unique site that includes the apical loop and the 5′ strand of the k-turn in the absence of L7Ae (B). L7Ae successfully competes with Cbf5 for binding to the 5′ strand of the k-turn and disrupts Cbf5s interaction with this region of the guide RNA (D).