Island biogeography

TLS Online TPP Program

#Id: 5044

#Unit 3. Fundamental Processes

Only fully methylated origins can initiate replication;

hemimethylated daughter origins cannot be used again until they have been restored to the fully methylated state.

TLS Online TPP Program

#Id: 5045

#Unit 3. Fundamental Processes

The GATC sites AT THE ORIGIN remain hemimethylated for 13 minutes after replication called as refractory period of replication cycle or delay time.

TLS Online TPP Program

#Id: 5046

#Unit 3. Fundamental Processes

At typical GATC sites elsewhere in the genome, remethylation begins immediately (1.5 minutes) following replication.

TLS Online TPP Program

#Id: 5047

#Unit 3. Fundamental Processes

One other region behaves like oriC:

The promoter of the dnaA gene also shows a delay before remethylation begins.

While it is hemimethylated, the dnaA promoter is repressed, which causes a reduction in the level of DnaA protein.

So Initiation of Replication (E.coli) takes place when GATC at origin is full methylated as well as promoter of DnaA gene. 

TLS Online TPP Program

#Id: 5048

#Unit 3. Fundamental Processes

An unmethylated CG site remains unmethylated after replication.

TLS Online TPP Program

#Id: 5049

#Unit 3. Fundamental Processes

DnaA is the E. coli licensing factor that must be made anew for each round of replication. Drugs that block protein synthesis block a new round of replication, but not continuation of replication.