Enhanced activation of transcription in Xtc1p-deficient yeast. β-Galactosidase activities in permeabilized yeast cells containing the following lacZ fusion reporter genes: lines 1 and 4, a single copy of the integrated plasmid RY171 (39), which contains Gal4-binding sites derived from the GAL1–10 UASg element upstream of the GAL1 core promoter; line 2, a 2-μ derivative of RY171; line 3, the 2-μ plasmid pJK101 (4), a derivative of RY171 in which the UASg is located a further 100 nt distal to the GAL1 promoter; and lines 5–7, the 2-μ plasmid p18–40 (4), which has a single LexA operator sequence upstream of the GAL1 core promoter. LexA-E2F-1 and LexA-GAL4 were expressed from the ADH1 promoter on 2-μ vectors (4). The strain used in line 4 had the MIG1 gene deleted. Cells were grown in the presence of 2% (wt/vol) galactose supplemented with either 2% (wt/vol) sucrose (lines 1–3, 5–7) or glucose (line 4) and were harvested at mid-log phase. Activities are expressed in Miller units (32); SD values were less than 20%.