Fig. 4. Overexpression of Sac3p or its C-domain causes a dominant-negative phenotype and an mRNA export defect. (A) Overexpression of full-length Sac3p or the C-domain is toxic. Wild-type cells transformed with the indicated plasmid-borne constructs were spotted in 10^–1 dilutions on a plate containing galactose (inductive for the GAL1 promoter). Growth was analyzed after 3 days at 30°C. (B) Overexpression of Sac3p, its C-domain or its N + M-domain causes an mRNA export defect. Poly(A)⁺ RNA localization was determined by in situ hybridization after 3.5 h induction of Sac3p expression in galactose-containing medium. Cells were also stained for DNA.