Figure 1. Rgt1 and Med8 proteins repress HXK2 expression in the absence of glucose.

(A) Hxk2 expression was measured by using the lacZ expression as reporter gene. One copy of the HXK2₊₄₀₄::lacZ, containing the Med8 binding downstream regulatory sequence (+DRS), or the HXK2₊₃₉::lacZ, lacking the Med8 binding downstream regulatory sequence (−DRS), constructs were integrated in the chromosome at URA3 locus of the wild-type strain DBY1315 or the mutant strain rgt1. β-Galactosidase activities are averages of the results obtained for four to five independent experiments. Average values have standard errors of 10% or less. Yeasts were grown on YEPD medium (open bars) or YEPE medium (solid bars) until the A₆₀₀ reached 1.0 [3.0 mg (wet weight)/ml]. β-Galactosidase activity was assayed in crude extracts. (B) Effect of RGT1 gene disruption on the expression of HXK2. A wild-type yeast strain (DBY1315) and the isogenic rgt1 mutant strain were grown using glucose (YEPD) or ethanol (YEPE) as carbon source as described above each lane. Total RNA was isolated, size-separated using a horizontal agarose gel and transferred on to a nylon membrane that was then hybridized to probes derived from HXK2 as described in the Materials and methods section. The probe used is indicated at the side of each panel.