Explain how the following mutations would affect transcription of the yeast GAL1 gene in the presence of galactose.

A deletion within the GAL4 gene that removes the region encoding amino acids 1 to 100.

Video transcript

Hi, everyone. Welcome back. Let's look at our next problem. It says Gal, for a modular protein, mainly consisting of the DNA binding domain and activation domain positively regulates the expression of galactose induced genes. Deletion of the gal four C terminus where the inhibitory protein gal 80 binds the Gal four region leads to. Well, this problem is rather tricky because we're talking about um gal for which positively regulates the expression of these genes. And we're talking about deleting the C terminus region of gal for which is where the inhibitory protein gal 80 binds to the gal for region. So it's a little tricky because our mind kind of jumps to automatically, well, the inhibitory protein can't bind then uh the gal four won't be inhibited and it will just be constantly turned on, constantly activated. So that would tend to lead us towards the answer. Choice of choice. A golfer retains its activation function. However, we have to recall what the structure of that Gal four gene is. And our clue comes from the beginning of this problem consisting of the DNA binding domain and the activation domain. So here's sort of our gal four gene we have up here is the end terminus on the left with the C terminus on the right. Well, the end terminus is the location of the DNA binding domain D B D. Then towards the sea term is that part of the gene is the activation domain A D here. So what we need to recall is that the area where gal 80 binds is also the activation domain. And I'm gonna draw a quick diagram of how that, how that actually looks as a structure just so we can kind of have a better picture in our head. So in my diagram, I've drawn the scenario where a gal four is bound to gal 80 that inhibitory protein. So here's the U S binding site and the promoter region of the gal genes. Here's our gal for protein, we have the DNA binding sites down here on the bottom bound to that us binding site. And then at the top here, we have the activation domain region of the gal for gene. And that is where the gal 80 is bound to that part of the gene, the C terminal area where the activation domain is, that makes sense because by blocking the activation domain, that's how Galati achieves its inhibitory effect. And of course, we know that I put over here gal three and galactose when galactose is present, galactose binds to the gal three, that changes Gal three's affinity for gal 80. Gal three then binds to gal 80 releasing it from gal four. So when gal four is bound to gal 80 have been inactive here, When galaxy is released, Gal four is now active and can go on and fulfill its positive regulatory function for those galactus genes. However, what we're asking a question about is if we delete that gal for C terminus. So in this case, we've deleted this region here. So it's true that gal 80 can no longer bind and achieve its inhibitory effect. However, without its activation domain Gal four Can no longer fulfill its activation function. So choice, a golfer retains its activation function is actually incorrect because gal for along with losing its ability to bind gal 80 has also lost its activation domain. So our answer here is going to be choice be gal four loses its interaction with gal 80 and its activation function. We looked at other answer. Choices. Choice C was both A and B since A is incorrect choice C is not our answer. Choice D says none of the above. Since choice B was correct, that's not our answer either. So again, the deletion of the Gal four C terminus where the inhibitory protein gal 80 binds to the gal for region leads to choice be golfer loses its interaction with Gal 80 and its activation function. See you in the next video.