Top Ten Reasons to Ask Questions During Class

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Top Ten Reasons to Ask Questions During Class
. . . . .
5) Your classmates likely have the same question
4) What I leave out may be important to you 3)
Discussions can be more informative than
lectures 2) It helps me to know what you arent
getting
And the Number One Reason to Ask Questions During
Class is
Its a great way to get me to slow down!
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Cdc2/Cyclin B (MPF) Regulates Mitosis
(CKIs)
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CDKs Regulate Many Cell Cycle Events
Another fortuitous discovery in Cell Cycle
Regulation
Synchronized cdc2ts cells cant initiate S-phase
Cdc2 drives entry into S-phase as well as Mitosis
How can one enzyme regulate multiple cell cycle
events?
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Cells Use Multiple Cyclins to Regulate Different
Events
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Growth Regulation in Yeast
Budding yeast grow in G1 - G1/S highly
regulated
Fission yeast grow in G1 - G2/M highly
regulated
S-phase regulation better understood in Budding
yeast - G1/S more highly regulated
From Susan Forsburg, Salk Institute
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Cdc28 is the Budding Yeast Cdc2 Homologue
- Cdc28 regulates entry into S-phase and
mitosis - Cdc28 is a protein kinase that
complements cdc2ts
Cdc28 is 63 Identical to Cdc2
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Cdc28 is the Budding Yeast Cdc2 Homologue
Is Cdc28 also a Cyclin-Dependent Kinase?
- How do you identify yeast cyclin genes?
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Cdc28 is the Budding Yeast Cdc2 Homologue
Is Cdc28 also a Cyclin-Dependent Kinase?
- How do you identify yeast cyclin genes?
Today Genome Sequence (Budding Yeast 1st
eukaryotic genome sequenced)
Yesteryear Homology (low stringency
hybridization) High Copy Suppression
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Budding Yeast Cyclin B-like Genes
Budding yeast has SIX Cyclin B-like genes
and NINE Cyclin genes in all
How Does One Kinase Control Multiple Processes?
One answer is multiple cyclins
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Budding Yeast Cyclin Genes
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Yeast Cyclin Genes Exist as Pairs
Chr VII
Chr XVI
Chr IV
Chr XIII
Chr XVI
Chr XII
Chr I
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Yeast Cyclin Gene Duplication
Duplication
Divergence
Duplication
Divergence
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Gross Overview of Cdc28 Function
Cdc28/Cln3 only pair present at M/G1 - drives
Cln1,2 and Cln5,6 transcription Cdc28/Cln1,2
drives START -indirectly activate
Cdc28/Clb5,6 Cdc28/Clb5,6 drives S-phase
entry Cdc28/Clb3,4 drives spindle
assembly Cdc28/Clb1,2 drives entry into Mitosis
All Cyclins are regulated by Ubiquitin-dependent
proteolysis
Cln3 is a possible exception
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The Budding Yeast Cell Cycle
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How do CDKs Regulate Multiple Transitions?
1) One mechanism is multiple cyclins
2) A second mechanism is the CKIs
(Cyclin-Dependent Kinase Inhibitors)
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Control of S-phase by Cdc28 in Budding Yeast
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Control of S-phase by Cdc28 in Budding Yeast
Sic1 is a CKI
Sic1 Prevents initiation of S-phase until
Cdc28/Cln1,2 is high enough to initiate Budding
and SPB duplication
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Control of S-phase by Cdc28 in Budding Yeast
Sic1 is a CKI
Sic1 Prevents initiation of S-phase until
Cdc28/Cln1,2 is high enough to initiate Budding
and SPB duplication
Sic1
Cdc28/ Cln1,2
Cdc28/ Clb5,6
DNA Rep.
Budding SPB Dup.
SPB
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Cdc28/Cln3 kinase
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CKI
Cyclin
CDK
T-Loop
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CKI
CKI
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Transcriptional Control
Ubiquitin-dependent Proteolytic Control
Wee1 kinases
Y15
Cdc25 phosphatases
Cyclin-dependent Kinase Inhibitors (CKIs)
T160
Cdk-Activating Kinases (CAK)
Kap1 phosphatses
transcriptional control
Phosphorylation Control
Adapted from Morgan (1997) Ann. Rev. CellDev.
Biol. 13261
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How is Re-replication of DNA Prevented?
Nurse screened for fission yeast mutants that
re-replicate DNA - ALL mapped to CDC2 and CDC13
(CDK and Cyclin B)
Cdc2 Both Launches S-phase and inhibits
re-replication
CDC2
cdc2ts
DAPI Staining
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How does Cdc2 Drive AND Inhibit Replication?
Model for Cdk control of S-phase Step 1 preRC
assembly (pre-Replication Complex) Step 2
activation of preRC - Step 1 requires Absence
of Cdk - Step 2 requires presence of
CDK Step 1 INHIBITED by CDK
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CDK Control of S-phase
STEP 1 Requires ABSENCE of MPF activity
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CDK Control of S-phase
STEP 2 Requires high CDK activity
Step 1 is INHIBITED through destruction of Cdc6
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CDK Control of S-phase
STEP 1 NO CDK
STEP 2 highg CDK
STEP 1 Inhibited
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Vertebrate Cells Express Multiple CDKs
Lodish et al. Figure 13-29
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Vertebrate Cells Express Multiple CDKs
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CDK Regulation via Subcellular Localization