This recombinational event is catalyzed by a set of enzymes, many of which are also involved in nonhomologous end joining (NHEJ) DNA repair functions that occur in all cells.

TLS Online TPP Program

#Id: 6018

#Unit 3. Fundamental Processes

As the transition from G1 to S phase begins, CDK/cyclins recruit cdc45 and the GINS complex to the MCM helicase, which then becomes known as the CMG complex (Cdc45-MCM-GINS)

TLS Online TPP Program

#Id: 6019

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6020

#Unit 3. Fundamental Processes

As cells enter into the S phase of the cell cycle, two kinases, CDK and DDK, are activated.  DDK phosphorylates loaded Mcm2-7 helicase, and CDK phosphorylates Sld2 and Sld3.Phosphorylated Sld2 and Sld3 bind to Dpb11, and together these proteins facilitate binding of the helicase-activating proteins, Cdc45 and GINS, to the helicase.  

TLS Online TPP Program

#Id: 6021

#Unit 3. Fundamental Processes

Cdc45 and GINS form a stable complex with the Mcm2-7 helicase (called the Cdc45/ Mcm2-7/GINS, or CMG, complex) and dramatically activate Mcm2-7 helicase activity.

TLS Online TPP Program

#Id: 6022

#Unit 3. Fundamental Processes

The leading-strand DNA polymerase (E) is recruited to the helicase at this stage (before DNA unwinding). After formation of the CMG complex, Sld2, Sld3, and Dpb11 are released from the origin. 

TLS Online TPP Program

#Id: 6023

#Unit 3. Fundamental Processes

DNA Pol a/ primase and DNA Pol d (which primarily act on the lagging strand) are only recruited after DNA unwinding.