Two major classes of actin-nucleating proteins:

1. Formins nucleate the assembly of unbranched filaments 

2. Arp2/3 complex nucleates the assembly of branched actin networks

TLS Online TPP Program

#Id: 8846

#Unit 2. Cellular Organization

In budding yeast CKI p27 = Sic1 in metazoans

TLS Online TPP Program

#Id: 8847

#Unit 2. Cellular Organization

When CDK activity is low= helicases are loaded in G1

When CDK activity is high= helicases are activated in

S, G2 & M

TLS Online TPP Program

#Id: 8848

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 8849

#Unit 2. Cellular Organization

Phosphorylation of MCM helicase activators by G1/S phase CDKs and S phase CDKs, prevents reloading of MCM helicases (ensuring that replication from each origin occurs only once during each cell cycle)

TLS Online TPP Program

#Id: 8850

#Unit 2. Cellular Organization

Geminin 

a small protein,, that contributes to the inhibition of re-initiation at origins until cells complete a full cell cycle.

TLS Online TPP Program

#Id: 8851

#Unit 2. Cellular Organization

Geminin is expressed in late G1; it binds to and inhibits Cdt1 preventing reloading of the MCM helicase.