Figure 4. ER stress triggered by misfolding of GFP is not the primary determinant of the expression limit of SS-GFP.

(A) Western blot analysis of SS-GFPs using anti-GFP antibodies. Protein samples were prepared from cells cultured in –Ura medium. Molecular weight (kDa) is shown on the left. DTT: dithiothreitol. (B) Growth of wild type (IRE1, BY4741) and ire1Δ cells upon high-level expression of modified GFPs. Cells expressing indicated modified GFPs were spread onto –Ura plates. (C) Copy numbers of modified GFPs in –Leu–Ura conditions. Error bars represent standard deviations. (D) Localization of modified GFPs. Arrowheads indicate aberrant and aggregated ER structures co-localizing with SS-GFP and SS-moxGFP. Percentages of normal two-ring ER structures observed with mRFP-Sec12 are also shown.