You have isolated another cDNA clone of the CRABS CLAW gene from ...

Question

You have isolated another cDNA clone of the CRABS CLAW gene from a cDNA library constructed using the vector shown in Problem 18. The cDNA was directionally cloned using the EcoRI and XhoI sites. You sequence the recombinant plasmid using primers complementary to the T7 and T3 promoter sites flanking the MCS (the positions of these sequences are shown in the figure in Problem 18). The first 30 to 60 bases of sequence are usually discarded since they tend to contain errors.

Will the long stretch of T residues in the T3 sequence exist in the genomic sequence of the gene?

Accepted Answer

Hi, everybody. Let's look at our next problem. The T three promoter sequence includes a series of T residues that create a poly T tract, which functions as a signal to halt transcription. Which of the following statements accurately describes the effects on the polymerase enzyme. When it comes into contact with the poly T tract. Choice. A, the polymerase enzyme pauses at the polyp tract. Choice B, the polymerase enzyme speeds up at the poly T tract choice C, the polymerase enzyme dissociates from the DNA at the poly T tract or choice D, the polymerase enzyme skips over the poly T tract. Well, if we can't remember off the top of our head, what it does? We can look and see that we have, our question tells us the poly T tract is a signal to halt transcription. So that can point us in the direction of our answer, which is choice A, that the polymerase has to pause at the poly T tract. And that is indeed our answer at that pot tract. It can cause the R N A polymerase to form a confirmation that can make it difficult to continue. So it's difficult for the R N A polymer to continue past this region. And then there's two possibilities, it may dissociate from the DNA template at this point or it may continue on after a halt. So let's look at our answer choices here. We have choice B that it speeds up. Well, that's pretty easy to rule out since we know it has a signal to halt transcription. Um Choice C the polymerase enzyme dissociates from the DNA. Um As we mentioned, this is a possibility it may do that but it might also just continue after a pause. So that's why choice C is not correct. So we'll say it may continue then choice. D the polymerase enzyme skips over the poly T tract. Well, this is not what happens. It doesn't skip it, it just sort of halts there for a little while. So again, as our question said, what accurately describes the effects on the polymerase enzyme when it comes into contact with the poly T tract? Choice. A the polymer enzyme pauses at the poly T tract. See you in the next video.

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