Unformatted text preview: n factor becomes an activator when combined with 1 protein and a
repressor when combined with 2 protein. Furthermore,
in a/ cells, a combination of the a1 and 2 proteins forms
a new transcriptional repressor whose binding to the promoters of haploid-speciﬁc genes represses their transcription with no requirement for the Mcm1 protein. Thus the
three cell types, in which several cell-type-speciﬁc genes
are expressed, arise from the activities of only three
speciﬁc proteins that bind directly to the promoters of
cell-type-speciﬁc genes to enhance or repress their transcription. Mating Type Switching
Yeast strains differ from each other according to the stability
of their mating type. Most laboratory strains have stable haploid mating types such that the progeny of successive mitotic
divisions always have the same mating type as their parents.
These strains with stable haploid mating types are known as
heterothallic strains. By contrast, strains that can switch
mating types are known as homothallic strains (Fig. A.11a).
In homothallic str...
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This note was uploaded on 10/03/2013 for the course BI 206 taught by Professor Celenza during the Spring '08 term at BU.
- Spring '08