Each set of ter sites allows a replication fork into the termination region, but does not allow it out the other side.For example, replication fork 1 can pass through terC and terB into the region, but it cannot continue past terE, -D, and -A. This arrangement creates a "replication fork trap."

TLS Online TPP Program

#Id: 764

#Unit 3. Fundamental Processes

Transition from CPC to OPC often called isomerization, does not require energy derived from ATP hydrolysis and is instead the result of a spontaneous conformational change in the DNA– enzyme complex to a more energetically favorable form.

TLS Online TPP Program

#Id: 765

#Unit 3. Fundamental Processes

The closed complex is converted into an open complex of 1.3 turns of the double helix in a series of steps by first “melting” a short region of DNA. 

This Isomerization is essentially irreversible and, once complete, typically guarantees that transcription will subsequently initiate.

TLS Online TPP Program

#Id: 766

#Unit 3. Fundamental Processes

Two bases in the non-template strand of the –10 element (A11 and T7) flip out from their base-stacking interactions and instead insert into pockets within the sigma protein where they make more favorable interactions for OPC

TLS Online TPP Program

#Id: 767

#Unit 3. Fundamental Processes

Abortive transcription is when RNA Polymerase makes short transcripts, typically shorter than 10 nucleotides (nt), while still bound at the promoter.

TLS Online TPP Program

#Id: 768

#Unit 3. Fundamental Processes

In abortive transcription, an RNA chain forms without movement of the enzyme down the template by scrunching DNA

 

TLS Online TPP Program

#Id: 769

#Unit 3. Fundamental Processes

After release of the abortive product, the enzyme again begins synthesizing RNA at position +1 called as Initiation