TABLE 1.

Epistatic relationships between RE^SCB, FKH1, CHL1, and yKU80

Strain	Genotype	% HML usagea
ECY401	MATa	71.5 ± 1.8
XW676	MATa REΔ	<10
ECY400	MATa RESCB	33.1 ± 2.2
ECY399	MATafkh1	34.0 ± 2.8
ECY398	MATachl1	51.8 ± 2.5
ECY494	MATa yku80	64.1 ± 1.1
ECY13	MATα	<10
ECY111	MATα chl1	<10
ECY397	MATa RESCBfkh1	17.7 ± 3.7
ECY396	MATa RESCBchl1	29.7 ± 3.9
ECY495	MATa RESCByku80	34.8 ± 2.1
ECY496	MATachl1 yku80	54.7 ± 4.6
ECY395	MATafkh1 chl1	14.4 ± 2.2
ECY497	MATafkh1 yku80	15.0 ± 1.4
ECY394	MATa RESCBfkh1 chl1	<10
ECY499	MATa RESCB fkh1 yku80	<10
ECY498	MATa RESCB chl1 yku80	17.8 ± 2.8
ECY500	MATa fkh1 chl1 yku80	14.3 ± 0.7
ECY501	MATa RESCB fkh1 chl1 yku80	<10
KS338	MATa 4A	65 ± 2
KS379	MATa 4A fkh1	<10
ECY177	MATa 4A chl1	54.4 ± 1.3

^aHML usage was determined in MATa strains carrying HMLα and HMRα-BamHI. Genomic DNA extracted from an entire population of cells in which mating-type switching has been induced was cut by BamHI and HindIII and probed with a Yα fragment.