Figure 1.

U3 wild-type snoRNA localizes to nucleoli regardless of the presence or absence of a cap. Fluorescein-coupled wild-type U3 small nucleolar RNA (WT U3) or the spliceosomal U2 small nuclear RNA (WT U2) or unincorporated fluorescein-UTP (FL-UTP) were injected into the nuclei of Xenopus laevis oocytes. After 2 h, nucleoli were prepared for visualization by phase-contrast (PC) or fluorescence microscopy. The nucleolar rDNA is stained blue by DAPI. In contrast to the control of U2 snRNA, fluorescein-labeled U3 snoRNA (FL, green) with a G-cap or A-cap or without a cap localizes to nucleoli. A lampbrush chromosome is visible in the bottom left of the phase-contrast and DAPI images of injected U2 snRNA. Bar, 10 μm.