Yeast Has Defined Origins S. cerevisiae ARS contains a conserved 11 bp ARS consensus sequence and multiple B elements ARS directs autonomous replication of plasmid DNA The ORC complex binds to the ARS during most of the cell cycle The S. pombe origin is larger and binds ORC by a distinct mechanism from Bell, Genes Dev. 16, 659 (2002)
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Yeast Has Defined Origins S. cerevisiae ARS contains a conserved 11 bp ARS consensus sequence and multiple B elements ARS directs autonomous replication.
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Yeast Has Defined Origins
S. cerevisiae ARS contains a conserved 11 bp ARS consensus sequence and multiple B elements
ARS directs autonomous replication of plasmid DNA
The ORC complex binds to the ARS during most of the cell cycle
The S. pombe origin is larger and binds ORC by a distinct mechanism
from Bell, Genes Dev. 16, 659 (2002)
Replication Origins in Metazoans
DNA replication initiates from distinct confined sites or extended initiation zones
The potential to initiate is modulated by sequence, supercoiling, transcription, or epigenetic modifications
from Aladjem, Nature Rev.Genet. 8, 588 (2007)
Initiation can influence initiation at an adjacent site
Some Features of Eukaryotic Replication Origins
from Méchali, Nature Rev.Mol.Cell.Biol. 11, 728 (2010)
Certain characteristics are common at metazoan replication origins but are not present at all origins
Different modules contribute to the selection of a given origin
Only a small subset of origins are active during a given cell cycle
Constitutive origins are used all the time and are relatively rare
Flexible origins are used to a different extent in different cells and follow the Jesuit Model “Many are called but few are chosen”
Inactive or dormant origins are only used during replication stress or during certain cellular programs
Different Classes of Replication Origins in Metazoans
from Méchali, Nature Rev.Mol.Cell.Biol. 11, 728 (2010)
Chromatin Structure Influences ORC Binding
from Méchali, Nature Rev.Mol.Cell.Biol. 11, 728 (2010)
Chromatin remodelling complexes can facilitate HAT binding
preRC proteins can be modified by HATs
Influence of Distal Elements on Initiation
from Aladjem, Nature Rev.Genet. 8, 588 (2007)
Deletion of DHFR promoter allows initiation to occur within the gene
Truncation of the DHFR gene confines initiation to the far end of the locus
Deletion of the -globin LCR prevents initiation within the locus
Deletion of the CNS1 sequence in the Th2 cluster do not initiate within the IL13 gene
The Formation of the preRC
Mcm2-7 is loaded as a double hexamer by ORC, Cdc6 and Cdt1
Sld3 and Cdc45 bind weakly to Mcm2-7
from Labib, Genes Dev. 24, 1208 (2010)
Mcm2-7 helicase is inactive until S phase
Origins Are Activated at Different Times
from Méchali, Nature Rev.Mol.Cell.Biol. 11, 728 (2010)
preRCs are formed during G1 on origins
Heterochromatic regions replicate later than euchromatic regions
The Replicative Helicase
Mcm2-7, Cdc45, and GINS (CMG complex) form the replicative helicase
from Moyer et al., Proc.Nat.Acad.Sci.USA 103, 10236 (2006)
Assembly of the Replicative Helicase
from Sheu and Stillman, Mol.Cell 24, 101 (2006)
preRC is formed during G1 by recruitment of Mcm2-7
Phosphorylation of MCM proteins by DDK recruits GINS and stabilizes Cdc45 association
from Remus and Diffley, Curr.Opin.Cell Biol. 21, 771 (2009)
Helicase Loading and Activation in DNA Replication
DnaA and ORC are structural homologs
Replication competence is conferred by Mcm2-7 loading and is prevented by inhibition of pre-RC proteins
CDKs prevent Mcm2-7 loading and are required for helicase activation
Activation of Helicase Requires Phosphorylation of Sld2 and Sld3
G1 CDKs allow Dbf4 to accumulate
DDK phosphorylates Mcm2-7 and promotes Cdc45 association
CDK phosphorylates Sld2 and Sld3 and promotes association with Dpb11