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Unformatted text preview: to repress aspeciﬁc genes. (b) In an a cell, Mcm 1 alone is the transcriptional
activator of a-speciﬁc genes. CEN Ya
MATα HMRa Yα Ya Mating type switching in homothallic strains. (a)
Homothallic strains are able to switch mating types. After production of an a / diploid through mating, the diploid can undergo
meiosis during sporulation, producing two a and two spores.
Progeny of these spores can switch to the opposite mating types
and mate back with a cell of opposite mating type. (b) Cassette
model of mating type switching. Three copies of mating type
information exist on chromosome III: HML, MAT, and HMR. Only
the information at the MAT locus is expressed. HML and HMR
contain the stored, silent information that can be copied into the
MAT locus. har06584_refA_001-020 11/13/06 09:12 PM Page 11 A.2 Cell Differentiation in Yeast: Mechanisms for Determining Cell Type The Roles of HML, HMR, and HO
in Mating Type Switching
The key to understanding the mechanism by which homothallic (HO) strain...
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- Spring '08