FIG. 5.

Site-specific phosphorylation determines ERF localization. (A) Ref-1 cells were transfected with a GFP-expressing plasmid (a and b) or with plasmids expressing GFP-ERF fusion proteins (c to j). The localization of the proteins was determined by the GFP fluorescence in exponentially growing cells (a, c, and e to j) or 1 h after serum withdrawal (b and d). (a and b) GFP; (c and d) GFP-ERF; (e) GFP-ERFmut1-2; (f) GFP-ERFmut3-4; (g) GFP-ERFmut7; (h) GFP-ERFmut1-5; (i) GFP-ERFmut3-7; (j) GFP-ERFmut1-7. (B) The localization of hybrid proteins expressed from the same plasmids as for panel A was scored in at least three different experiments. The values are the averages from at least 100 positive cells. Cells with proteins localized exclusively in the nucleus or in the cytoplasm were scored in the respective category. Ubiquitous distribution includes cells with detectable fluorescence in both compartments even when the distribution was not even.