about this presentation includes introduction of yeast and there types of mating and switching.

1. MATING TYPES OF YEAST
PRESENTED BY
SNEHAL G PACHPOR
M.Sc MICROBIOLOGY Ist YEAR
(SEMESTER I)
PAPER IV
MEMBRANE STRUCTURE
AND SIGNAL TRANSDUCTION

2. CONTENT
 INTRODUCTION
 MATING TYPES OF YEAST
 THE LIFE CYCLE OF SACCHAROMYCES
CERVISIAE
 DIFFERENCES BETWEEN a AND α CELLS
 DIFFERENCES BETWEEN HAPLOID AND
DIPLOID CELLS
 MATING TYPE SWITCHING
 MECHANICS OF THE MATING TYPE SWITCH

3.  Yeast are eukaryotic microorganism classified in the
kingdom fungi , with 1500 species currently described.
 Yeast are unicellular organism but some species have
the ability to develope multicellular charecterstics.
 Yeast size can depend on the species typically
measuring 3-4µm in diameter.
 Most yeast reproduce asexually by mitosis , and many
do so by an asymmetric division process called
budding.
 The yeast speices Sacchromyces cerevisiae convert
carbohydrates to carbon dioxide and alcohols , carbon
dioxide has been used in baking and the alcohol in
alcoholic beverages.

4. LIFE CYCLE OF SACCHAROMYCES CEREVISIAE
 S.Cerevisiae (yeast) can stably exist as either a diploid or
haploid.
 Both haploid and diploid yeast cells reproduce by mitosis,
with daughter cells budding off of mother cells.

5. DIFFERENCES BETWEEN Α AND ALPHA CELLS
 A cells produce ‘ a-factor’, a mating
pheromones which signals the presence of
an a cell to neighbouring α cells. a cells
respond to α factor.
 Simillarly, α cells produce α-factor, and
respond to a-factor by growing a projection
towards the source of the pheromene.
 Phenotypic differences between a and α
cells are due to a different set of genes, a
cells activate genes which produce a-factor
and produce a cell surface receptor.
 Similarly, α cells activate genes which
produce α-factor and produce a cell surface
receptor.
 The different sets of trascriptional repression
and activation are caused by the presence
of one of two alleles of a locus called MAT:
MAT a or MAT α located on chromosome III.
 The MAT a allele of MAT encodes a gene
called a1.
 The MAT α allele of MAT encodes the α1
and α2 genes.

6. DIFFERENCES BETWEEN
HAPLOID AND DIPLOID CELLS
 Haploid cells are one of the
two mating types(a or α)
 The different haploid a and
α cells, different patterns of
gene repression and
activation are responsible
for the phenotypic
differences between haploid
and diploid cells.
 Similarly, diploid cells
activate diploid-specific
genes and repress haploid-
specific genes.

7. MATING TYPE SWITCHING
 Haploid yeast are
capable of switching
mating type between a
and α.
 A single haploid cell of a
given matting type founds
a colony if yeast.
 Mating type switching will
cause cells of both a and
α mating types to be
present in the population.

8. HML AND HMR: THE SILENT
MATING CASSETTES
 The HML( Hidden MAT Left) locus typically carries a
silenced copy of the MATα allele, and the HMR (Hidden
MAT Right)locus typically carries a silenced copy of
the MATa allele.
 The silent HML and HMR loci are often referred to as
the silent mating cassesttes.
 A haploid cell with the MATa allele present at the
active MAT locus is still an a cell, also having a
(silenced) copy of the MATα allele present at HML.

9. MECHANICS OF THE MATING TYPE SWITCH
 The process of mating type switching is a gene
conversion event initiated by the HO gene. The HO gene
is a tightly regulated haploid specific gene that is only
activated in the haploid cells during the G1 phase of the
cell cycle.
 The protein encoded by the HO gene is a DNA
endonuclease, which physically cleaves DNA, but only at
the MAT locus (due to the DNA sequence specificity of
the HO endonuclease).

10. REFERENCES
Molecular Cell Biology Edition,
WH Freeman and Col,NY.ISBN 0-716-4366-3

11. THANK YOU