The E. coli oriC is fully methylated at the beginning of replication.

TLS Online TPP Program

#Id: 5053

#Unit 3. Fundamental Processes

DnaA has a weak ATPase intrinsic activity which is enhanced by a factor termed Hda.

In a conceptually elegant feedback loop, Hda is recruited to a replication origin via the b subunit of the DNA polymerase. it acts to switch off DnaA

TLS Online TPP Program

#Id: 5054

#Unit 3. Fundamental Processes

Phospholipids promote the exchange of ATP with ADP bound to DnaA

TLS Online TPP Program

#Id: 5055

#Unit 3. Fundamental Processes

DnaA then acts at three A-T–rich 13-bp tandem repeats located on the left side of oriC.

TLS Online TPP Program

#Id: 5056

#Unit 3. Fundamental Processes

Initiation of replication at oriC starts with formation of a complex that ultimately requires six proteins: DnaA, DnaB, DnaC, HU, gyrase, and SSB.

TLS Online TPP Program

#Id: 5057

#Unit 3. Fundamental Processes

Two to four monomers of DnaAATP bind at the origin, and after release of DiaA, they recruit two “pre-priming” complexes of the DnaB helicase bound to DnaC-ATP, so that there is one DnaB–DnaC-ATP complex for each of the two (bidirectional) replication forks.

TLS Online TPP Program

#Id: 5058

#Unit 3. Fundamental Processes

Each DnaB–DnaC complex consists of six DnaC monomers bound to a hexamer of DnaB.

Note that the DnaB helicase cannot open double-stranded DNA; it can only unwind DNA that has already been opened, in this case by DnaA.

DnaB binding to single-stranded DNA is the signal to hydrolyze ATP and for release of DnaC.