FIGURE 6.

Utp10 and Utp20 are concentrated in the nucleolus but do not shuttle between nuclei in a heterokaryon assay. (A) At steady state, Utp10-GFP localizes to the nucleolus, and Utp20-GFP is present in the whole cell but is enriched in the nucleolus. Cells were fixed, DAPI stained, and viewed by fluorescence microscopy. (B) Utp10-GFP does not shuttle from the nucleus to the cytoplasm. Strains expressing Utp10-GFP, Utp20-GFP, and Arx1-GFP were grown in YPD media, mated with a kar1-1 mutant strain, and incubated at 25°C until heterokaryons formed. Localization of the GFP-tagged proteins in heterokaryons is shown for Arx1-GFP (upper panel), Utp10-GFP (middle panel), and Utp20-GFP (lower panel). Cells are shown with DAPI-stained nucleoplasm. Arrows indicate the positions of nuclei in the heterokaryons. (C) Utp20-GFP does not rapidly shuttle from the nucleus to the cytoplasm. One nucleus from each heterokaryon expressing either Arx1-GFP or Utp20-GFP was bleached. The recovery of fluorescence of the bleached nuclei was followed during a time course after bleaching. Arrows indicate the position of the targeted nucleus.