FIG. 6.

(A) Glucose induction of HGT12, HXT10, and HGT7 is dependent on HGT4. Cells were grown to log phase (OD₆₀₀ = 0.5 to 1.0) and then incubated for 2.5 h in 5% glycerol (gly) or with the indicated levels (%) of glucose. Cells were harvested, total RNA was prepared, and RT-PCR was performed on the indicated targets (see Materials and Methods). The strains used were wild-type CM49 and hgt4Δ CM137. Control reactions lacking reverse transcriptase produced no PCR products (data not shown). (B) High levels of glucose repress the expression of HGT4, HGT12, and HXT10 but not HGT7. Cells (CM49) were incubated for 2.5 h with the indicated level of glucose (%). RT-PCR analysis of the indicated target genes is shown. (C) Hgt4 acts through the transcriptional repressor Rgt1. Deleting the RGT1 gene restored the expression of HGT12 and HGT7 in the hgt4Δ mutant. RT-PCR analysis compared the expression of Hgt4-target genes in wild-type DAY286 cells (induced expression) versus hgt4Δ mutant CM9 cells (uninduced expression) versus hgt4Δ rgt1Δ double mutant CM170 cells (constitutive expression). Cells were induced for 2 h in 0.05% glucose. Total RNA was extracted, and RT-PCR was performed as described in the text.