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Unformatted text preview: s switch mating type came from the
discovery of two additional copies of the MAT locus called
HML and HMR. Located near the telomeres on each arm of
chromosome III, the HML and HMR loci are transcriptionally silent.
In wild-type strains, HML contains information and
HMR contains a information. The mechanism of mating
type switching involves a transposition of mating type information from the transcriptionally silent HML or HMR
locus into the transcriptionally active MAT locus. Switching occurs only in the a and cell types. a/ cells do not
switch even if they carry HO because the a1 and 2 regulators repress transcription of the HO gene.
A simple way to understand the mechanism of mating
type switching in homothallic strains is to imagine an analogy with a cassette tape recorder. A cell can retrieve a cassette of mating type information located in an HML or
HMR storage locus and insert it into the MAT playback locus. The cell retrieves information from the storage locus
by a series of steps. The product of the HO gene, a sitespeciﬁc endonuclease, initiates the process. The HO-encoded
enzyme makes a double-stranded cut in chromo...
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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