Nitrogenase is a complex consisting of the MoFe protein (dinitrogenase or component I) a heterotetramer, and the Fe protein (dinitrogenase reductase or component II) a homodimer.

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.

TLS Online TPP Program

#Id: 5059

#Unit 3. Fundamental Processes

Two-state assembly model of bacterial replication initiation

TLS Online TPP Program

#Id: 5060

#Unit 3. Fundamental Processes

Input of energy in the form of ATP is required at several stages for the prepriming reaction, and it is required for unwinding DNA.

The helicase action of DnaB depends on ATP hydrolysis, and the swivel action of gyrase requires ATP hydrolysis.

ATP also is needed for the action of primase and to load the b subunit of Pol III in order to initiate DNA synthesis.

TLS Online TPP Program

#Id: 5061

#Unit 3. Fundamental Processes

SeqA binds to hemimethylated DNA and is required for 13 min delaying rereplication.