Fig. 4. snoRNAs localize to nucleoli in Ran mutant strains. The subcellular distribution of U3 and snR10 snoRNAs and poly(A)+ RNA were determined by fluorescence in situ hybridization using Cy3-labeled U3, snR10 and oligo d(T) probes as indicated. FISH analysis was performed in a strain containing a temperature-sensitive mutation in Ran (gsp1-1) or a double mutant (gsp1-1 rbp1-1) containing also a temperature-sensitive mutation in the large subunit of RNA polymerase II required for production of poly(A)+ mRNA. Cells were analyzed both at 25°C (permissive temperature) and after a shift to the non-permissive temperature of 37°C for three hours. The merged image shows the position of each RNA relative to the DAPI-stained nucleoplasmic signal. U3 and snR10 nucleolar signals are observed in both strains at both permissive and non-permissive temperatures. As expected, export of poly(A)+ RNA to the cytoplasm is blocked at the non-permissive temperature.