FIG. 4.

GCN4 transcription or translation in yeast cells expressing α₁β₁ Na,K-ATPase, α₁(TM4/TM5), or an empty expression vector. The S288C mutant (A) or W303 (B) strain carrying the translational GCN4-lacZ reporter fusion, the S288C mutant strain carrying the GCN4^Δuorf-lacZ fusion (C) and a plasmid for galactose-inducible expression of α₁β₁ Na,K-ATPase or α₁(TM4/TM5) or an empty vector, and the W303 strain carrying the translational GCN4-lacZ reporter fusion and a plasmid for tetracycline-inducible expression (D) of Na,K-ATPase or the empty vector were grown in amino acid-supplemented minimal medium at 30°C as described in Materials and Methods. At an OD₄₅₀ of 1, each culture was induced with 2% galactose (A, B, C) or various concentrations of doxycycline (D) dissolved in growth medium lacking glucose but containing amino acids. For panels A, B, and C, specific β-galactosidase activities 0, 4, 24, 48, and 72 h after induction were determined in purified cytosolic fractions. For panel D, β-galactosidase activities were determined 24 h after induction with doxycycline. Data are given as mean values ± standard deviations from three independent growth experiments with double determinations of each data point (A, B, D) or as mean values from two independent growth experiments with double determinations of each data point (C).