Fig. 8. Thp1p is located at the nuclear envelope and required for mRNA export. (A) GFP-tagged Thp1p exhibits a nuclear envelope staining, which is lost in sac3Δ and nup1Δ cells. Cells were analyzed by fluorescence microscopy and by Nomarski optics. (B) Deletion of THP1 causes growth inhibition and inhibition of mRNA export. Serial dilutions of thp1Δ and wild-type cells were spotted onto YPD plates and grown for 4 days at the indicated temperatures (upper panel). Poly(A)⁺ RNA accumulates in the nucleus of thp1Δ cells at 23 and 37°C (lower panel). (C) SSA1 mRNA accumulates in the nucleus of sac3Δ and thp1Δ cells. Cells were shifted to 42°C for 30 min to induce the expression of the SSA genes, and localization of the SSA1 transcript was assessed in comparison to mex67-5 cells by in situ hybridization with a fluorescently labeled probe specific for SSA1 mRNA.