Fig. 5

Formation of Med15 nuclear foci is mediated by its IDR and a hydrophobic amino acid sequence. a Diagrams of mouse Med15 truncation mutants examined in this study. TagRFP was fused to the N-terminus of each protein fragment. SV40 NLS (NLS*, orange) was inserted before the coding regions of several Med15 truncation mutants at their N-termini. The endogenous NLS (blue) of mouse Med15 is located at amino acid residues 661-670. b Representative images of NIH3T3 cells expressing each mouse Med15 truncation mutant fused to TagRFP. Scale bar: 5 μm. c Percentages of NIH3T3 cells that display no nuclear clusters, small nuclear clusters (diameter < 1 μm), and large nuclear clusters (diameter > 1 μm) of mouse Med15 (WT) or truncation mutants. The numbers of analyzed cells were 90, 88, 96, 117, 92, and 85, respectively. The numbers of cells without clusters and the numbers of cells with clusters (including small and large) were obtained for each construct and subject to Fisher’s exact test: *** indicates p < 0.001. d Percentages of cells that display no clusters or nuclear clusters among NIH3T3 cells expressing GFP-mMed15 (WT) (n = 73) or GFP-mMed15 (mutant) (n = 164). This Med15 mutant contains eight point mutations within the 639-660 region which convert hydrophobic amino acids into hydrophilic amino acids (shown in the sequence comparison above the plot). Fisher’s exact test: p < 0.001 (indicated by ***). e Representative images of NIH3T3 cells expressing AcGFP-tagged mMed15 (WT) protein and the Med15 mutant described in d. The right columns contain the enlarged images of cells marked with dashed white borders. Scale bars: 5 μm. Similar results were obtained from two independent experiments