Italian physician Francesco Redi (1626–1697),

His hypothesis was supported when maggots developed in the uncovered jars, but no

maggots appeared in either the gauze-covered or the tightly sealed jars. He concluded that

maggots could only form when flies were allowed to lay eggs in the meat, and that the

maggots were the offspring of flies, not the product of spontaneous generation.

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.

TLS Online TPP Program

#Id: 5050

#Unit 3. Fundamental Processes

DnaA is an ATP-binding protein.

The first stage in initiation is binding of the DnaA-ATP protein complex to the fully methylated oriC sequence.

This takes place in association with the inner membrane. DnaA is in the active form only when bound to ATP.

DnaA has intrinsic ATPase activity that hydrolyzes ATP to ADP and thus inactivates itself when the initiation stage ends.

TLS Online TPP Program

#Id: 5051

#Unit 3. Fundamental Processes

DnaA ATPase activity is stimulated by membrane phospholipids and single-stranded DNA.