Following statements are regarding to maternally provided mRNAs—hunchback and caudal, are critical for patterning the anterior and posterior regions of the body plan, respectively.

A. These two mRNAs are synthesized by the nurse cells of the ovary and transported to the oocyte, where they are distributed ubiquitously throughout the syncytial blastoderm.

B. Translation of the hunchback and caudal mRNAs is repressed by the diffusion gradients of Bicoid and Nanos proteins, respectively.

C. Bicoid binds to a specific region of caudal’s 3′UTR. Here, it binds Bin3, a protein that stabilizes an inhibitory complex that prevents the binding of the mRNA 5′ cap to the ribosome. By recruiting this translational inhibitor, Bicoid prevents translation of caudal in the anterior of the embryo.

D. Nanos protein prevents translation of the hunchback message. Nanos in the posterior of the embryo forms a complex with several other ubiquitous proteins, including Pumilio and Brat. This complex binds to the 3′UTR of the hunchback message, where it recruits d4EHP and prevents the hunchback message from attaching to ribosomes.

Which of the following statements are true?

#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.

#Question id: 4460

#Unit 3. Fundamental Processes

During initial transcription, the active center of RNA polymerase is translocated forward relative to the DNA template and synthesizes short transcripts before aborting, then repeats this cycle until it escapes the promoter. Three models have been proposed to account for this;

i. Polymerase moves along the DNA.

ii. The front part of the enzyme moves along the DNA, but because of a flexible region within the enzyme, the back part of the enzyme can remain stationary at the promoter.

iii. The enzyme remains stationary and pulls the DNA into itself.

#Question id: 4461

#Unit 3. Fundamental Processes

According to some experiments, during initial transcription, the polymerase remains stationary on the promoter, unwinds downstream DNA, and pulls that DNA into itself, which model is this?

#Question id: 4462

#Unit 3. Fundamental Processes

Promoter escape is associated with the breaking of all interactions (at the given promoter) between;

#Question id: 4463

#Unit 3. Fundamental Processes

___?____ is a way to store and mobilize energy during transcription initiation, and its release upon escape is what enables polymerase to break free of the promoter and dislodge s factor from the core.

#Question id: 4464

#Unit 3. Fundamental Processes

Role of Gre factor;