#Question id: 4454
#Unit 3. Fundamental Processes
Correct series of sigma regions,
#Question id: 4455
#Unit 3. Fundamental Processes
The __I is connected to the II by a flexible linker, although the II is embedded in the body of the enzyme, the I can reach the upstream element and can do so even when that element is not located immediately adjacent to the –35 region, but further upstream.
#Question id: 4456
#Unit 3. Fundamental Processes
Correct statement about two striking structural changes are seen in the enzyme upon isomerization from the closed to the open complex;
A. First, the pincers at the front of the enzyme clamp down tightly on the downstream DNA.
B. Second, there is a major shift in the position of the amino-terminal region of s. When not bound to DNA, s region 3.2 lies within the active center cleft of the holoenzyme, blocking the path that, in the open complex, is followed by the template DNA strand.
C. In the open complex, region 1.1 shifts some 50 A˚ and is now found on the outside of the enzyme, allowing the DNA access to the cleft.
D. Region 1.1 of s is highly negatively charged ( just like DNA).
#Question id: 4457
#Unit 3. Fundamental Processes
In the holoenzyme, which sigma region acts as a molecular mimic of DNA?
#Question id: 4458
#Unit 3. Fundamental Processes
What structural changes will occur at the time of transition to the open complex and how we describe this transition in transcription,
#Question id: 4459
#Unit 3. Fundamental Processes
Give correct explanation, why RNA polymerase can initiate a new RNA chain on a DNA template without any primer?
A. Because RNA polymerase starts most transcripts with an A, and that ribonucleotide binds the template nucleotide (T) with only two hydrogen bonds.
B. The enzyme has to make specific interactions with one or all of the DNA template strand, the initiating ribonucleotide, and the second ribonucleotide—holding one (or all) rigidly in the correct orientation to allow chemical attack on the incoming NTP.
C. The structure of the open complex shows that the s region 3/4 linker interacts with the template strand, organizing it in the correct conformation and location to allow initiation.
D. Consistent with this, in experiments using an RNA polymerase containing a s70 derivative lacking this part of s, initiation requires much lower than normal concentrations of one or both of the first two ribonucleotides.