TABLE 3.
Constitutive activities of α-factor receptor mutants
| Receptor | β-Galactosidase activity (U)a | Fold increase in basal activityb | Basal activity relative to maximum α-factor-induced activityc |
|---|---|---|---|
| Wild-type STE2 | 2.7 ± 0.2 | 3.8 | |
| S251L | 1.5 ± 0.1 | 0.5 | 2.0 |
| C252L | 1.4 ± 0.1 | 0.5 | 1.9 |
| Q253L | 13.7 ± 0.6 | 4.9 | 19.0 |
| S254L | 2.1 ± 0.1 | 0.7 | 2.9 |
| S254F | 6.6 ± 0.7 | 2.4 | 9.2 |
| S259L | 2.5 ± 0.1 | 0.9 | 3.4 |
a
Basal signaling activities in yeast strain JKY79 carrying the indicated receptor genes on a plasmid were assayed. The activity of a FUS1-lacZ reporter gene was determined by quantifying β-galactosidase activity. Results are the averages of two to six independent assays, each done in duplicate (± standard deviations).
b
Ratio of mutant basal activity to wild-type basal activity.
c
Comparison of the ligand-independent basal activities of the mutants to the maximum ligand-induced activities of wild-type cells treated with 10−6 M α-factor (72.1 ± 1.7 U).