Role of evolutionarily conserved box H and box ACA in nucleolar localization of U17 snoRNA. U17 snoRNA carrying a substitution (sub. box H) or deletion (Δbox H) of just conserved box H alone retained the ability to localize to nucleoli, resulting in moderate to strong nucleolar labeling. Nucleolar localization signals with mutants substituted in box ACA, deleted in the ACA region (Δbox ACA+), or substituted in the ACA region (sub. box ACA+) were highly variable. The double mutants of box H and the box ACA region, being either depleted (Δbox H/Δbox ACA+) or substituted (sub. box H/sub. box ACA+) in both sequences, were not capable of localizing to nucleoli. Nucleolar localization was also abolished when the deletion of box H was coupled with the deletion of just box ACA itself (Δbox H/Δbox ACA). A combination of the deletion of stem 2 and box H (Δ46–108/Δbox H) did not enhance the effect of a stem 2 deletion alone (see Figure 3), and localization was still apparent. Bar, 10 μm.