#Question id: 4539

The yeast S. cerevisiae exists in three forms: two haploid cells of different mating types—a and alpha and the diploid formed when an a and an a cell mate and fuse. The a cell and the a cell each encodes cell-type-specific regulators: a cells make the regulatory protein a1, and alpha cells make the proteins alpha1 and alpha2. A fourth regulatory protein, called Mcm1, is also involved in regulating the mating-type-specific genes (and many other genes) and is present in both cell types which shows Combinatorial Control.

The arrangement of regulators at the promoters of a-specific genes and a-specific genes is

cell type:	gene regulatory proteins:	target genes:
1.a cell (haploid)	a1 Mcm1	aSG alphaSG
2.αlpha cell (haploid)	alpha 1 alpha 2 Mcm2	hSG
3.a/αlpha cell (diploid)	a1 Mcm2 alpha2