Table 3.

Effects of substitutions of proline-222 in TMS VI of the a-factor receptor

STE3 allele	FUS1-lacZ expression (% wild type +a-factor)
	−a-factor	+a-factor
ste3Δ	40 ± 6	40 ± 6
wild-type	32 ± 7	100 ± 9
P222L	60 ± 10	72 ± 8
P222F	60 ± 11	76 ± 3

The indicated STE3 alleles were overexpressed from their normal promoters on high copy plasmids (pRS425 derivatives) in a ste3Δ mfa1Δ mfa2Δ sst2Δ strain (SY1985) that contained an integrated FUS1-lacZ reporter. Where indicated, cells were diluted 1:1 with culture fluid from MATa cells (source of a-factor), incubated 2 h at 30° and assayed for β-galactosidase activity. Data are expressed as a percent of the activity detected using a-factor-treated cells that expressed the wild-type STE3 gene. At least four independent transformants of each type were assayed in duplicate; standard errors are indicated.