Affiliation:
1. Department of Biology and Rosenstiel Basic Medical Sciences Research Center Brandeis University, Waltham, MA 02454-9110
Abstract
ABSTRACT
The budding yeast
Saccharomyces cerevisiae
has two alternative mating types designated
MAT
a
and
MAT
α. These are distinguished by about 700 bp of unique sequences, Y
a
or Yα, including divergent promoter sequences and part of the open reading frames of genes that regulate mating phenotype. Homothallic budding yeast, carrying an active HO endonuclease gene,
HO
, can switch mating type through a recombination process known as gene conversion, in which a site-specific double-strand break (DSB) created immediately adjacent to the Y region results in replacement of the Y sequences with a copy of the opposite mating type information, which is harbored in one of two heterochromatic donor loci,
HML
α or
HMR
a
. HO gene expression is tightly regulated to ensure that only half of the cells in a lineage switch to the opposite
MAT
allele, thus promoting conjugation and diploid formation. Study of the silencing of these loci has provided a great deal of information about the role of the Sir2 histone deacetylase and its associated Sir3 and Sir4 proteins in creating heterochromatic regions.
MAT
switching has been examined in great detail to learn about the steps in homologous recombination.
MAT
switching is remarkably directional, with
MAT
a
recombining preferentially with
HML
α and
MAT
α using
HMR
a
. Donor preference is controlled by a
cis
-acting recombination enhancer located near
HML
. RE is turned off in
MAT
α cells but in
MAT
a
binds multiple copies of the Fkh1 transcription factor whose forkhead-associated phosphothreonine binding domain localizes at the DSB, bringing
HML
into conjunction with
MAT
a
.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Cell Biology,Microbiology (medical),Genetics,General Immunology and Microbiology,Ecology,Physiology
Cited by
54 articles.
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