Table D lists α-globin and β-globin gene sequences for t...

Question

Table D lists α-globin and β-globin gene sequences for the 11 or 12 nucleotides preceding the start codon and the first nucleotide following the start codon (see Problem 34). The data are for 16 vertebrate globin genes reported by Kozak (1987). The sequences are written from -12 to +4 with the start codon sequence in capital letters. Use the data in this table to

Determine the consensus sequence for the 16 selected α-globin and β-globin genes.

Accepted Answer

Welcome back everyone. Let's look at our next answer choice. It says in a study, a researcher has identified the binding sites of a transcription factor in several genes. They have aligned the DNA sequences of these binding sites and generated a consensus sequence. The consensus sequence for the binding site is shown below. And we have five prime T G T A and then a series of five letter NSS and then A T C A CAA three prime using the consensus sequence predict which of the following sequences is most likely to be a binding site for this transcription factor. And then we have four answer choices, each of which is a different DNA sequence all about the same length as our consensus sequence shown above. And one thing that's important to note is that all are written in the five prime to three prime direction. Sometimes with multiple choice problems like this, they try and trip you up by listing some in the three prime to five prime direction. So you always want to make sure you're comparing them in the same direction. So let's take a look at our consensus sequence. Of course, those ends represent nucleotides. That could be anything. The identity of those nucleotides doesn't affect the ability of the transcription factor to bind. And we want to look for the closest match to our consensus sequence. So we've got specific bases on the five prime end and specific bases on the three prime end. So let's start with the bases on the five prime end. Those first four bases are T G T A. So let's compare that to the first four bases in our four answer. Choices in choice A, the first four are T G T A. So choice A is definitely a possibility as it's an exact match there at the end. Choice B is A G T A. So that's off by one. So I'm just gonna mark that there. I'm not gonna eliminate it just yet because we do want to look at the bases on the three prime end because it could be that even though choice A is an exact match on the five prime end, perhaps it's just completely off on the three prime end. And the question is trying to trip us up by giving us that exact match at the beginning. Jo C is T C G T. So this is off by two here. So probably not our answer choice. And then choice D, the first four bases are T C T A. So off by a single base there in the second position. So choice A is looking pretty good but again, we want to take a look at those bases at the three prime end to make sure that we don't have a closer match when we bring them into the consideration. So let's look at our three prime end. So our seven bases here in the consensus sequence, we have a T C A CAA, but I kind of want to work backwards because of course, we have all those ends in the middle that it doesn't matter what they are. So it's a little easier to start from the three prime end. So let's look at choice A and see what that is. So starting from a three prime end A AC, so that's an exact match and then AC T A which also is an exact match. So I've now got choice a being an exact match for every single nucleotide since BC and D already have mismatches. I don't even need to look at their three high end. I can go ahead and pick choice A as my answer here since it's a perfect match to our given consensus sequence. So it will be most likely to be a binding site for that transcription factor. So again, that sequence most likely to be a binding site choice A which is five prime T G T A G G A T A A T C A CAA three prime. See you in the next video.

Key Concepts

Consensus Sequence

Start Codon

Kozak Sequence

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