FIG. 11.

Transactivation of HIS4 gene in response to heterologous expression. Yeast cells carrying the transcriptional HIS4-lacZ fusion and an expression plasmid for α₁β₁ Na,K-ATPase or α₁(TM4/TM5) or the empty expression vector were grown and induced as described in Materials and Methods. Specific β-galactosidase activities were determined in isolated cytoplasmic fractions of cells harvested 0, 4, 24, 48, or 72 h after induction. A culture containing the empty vector was supplemented or not with 3-AT and harvested after 24 h. Specific β-galactosidase activities were determined in purified cytosolic fractions from three independent experiments with triple determinations of each data point.