Molecular Cell Biology of the Yeast

Saccharomyces cerevisiaeLecture III: Molecular Logic of Asymmetry

Zhang Yi,

National Institute of Biological Sciences, 20080628

Cellular Anatomy

Mitosis V.S Meiosis

α

α

a

a

Mating Type Switch

Mating Type Specific Gene

• MATa gene expression– a1 mRNA from MATa locus– Other a-specific gene expression is

default• Driven by MCM1 homodimer

• MAT gene expression 1, 2 mRNA from MAT 1 and 2 function

• Repress a-specific genes 2/MCM1 heterodimer

• Stimulate -specific genes 1/MCM1 heterodimer

Mating Type Specific Gene Expression

Mating Type Switch Mechanism: HO

Mating Type Switch Mechanism: hetero-sequence switch

Recombination Enhancer Sequence

Sequence-Specific RE Effects

RE Sequence Shows MatAlpha2 Binding Site

RE Mutants Render Chromatin Structural Change

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wt

mt

A Mcm1p Binding Site in RE is Necessary for RE Function

MatAlpha2 Interaction with Tup1/Ssn6 is Essential for Haploid/a-specific Gene Repression

Tup1/Ssn6 Complex is Global Transcription Suppressor Associated with HDACs

A Model Summarizing Mcm1p-Mediated Chromosomal Effects on RE and Other Loci

Evolution of the Molecular Logic of Mating Type in Fungi

S.Pombe

Maternal Effect on Mating Type Switch

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HO Promoter Dissection

HO Expression Depends on Swi/Snf Complex: LOF and GOF

Ash1p Represses Mating Type Switch in Daughter Cell by Inhibiting HO Expression

Ash1p and Swi/Snf Show Reciprocal Effects on Mating Type Switch

Ash1p Localization Dependence: Genetic Screen

Screen for mother cells who do NOT express HO (promoter is inhibited) as a consequence of any genetic defect

She Genes are Necessary for HO Expression

She1p/5p are Cytoskeletal Proteins, and Some She Genes are Localized to Daughter Cells

Interdependence of She genes on localization

Actin-dependent Ash1 mRNA Localization into Daughter Cell

FISHPharmacology

LOF

GeneticsLOF

GeneticsGOF

She genes and Ash1 mRNP transport

Visualizing mRNA Transport

Local Translation

Local Translation Regulation is as Essential as Localization

Protein Level in Temporal Context

Degredation for old alpha2 as well as HO etc

Protein Dynamics not Limited to Ash1 mRNA Transportation