DNA methylation is commonly associated with a reduction of transcription. The following data come from a study of the impact of the location and extent of DNA methylation on gene activity in eukaryotic cells. A bacterial gene, luciferase, was inserted into plasmids next to eukaryotic promoter fragments. CpG sequences, either within the promoter and coding sequence (transcription unit) or outside of the transcription unit, were methylated to various degrees, in vitro. The chimeric plasmids were then introduced into cultured cells, and luciferase activity was assayed. These data compare the degree of expression of luciferase with differences in the location of DNA methylation [Irvine et al. (2002). Mol. and Cell. Biol. 22:6689–6696]. What general conclusions can be drawn from these data? 

Video transcript

Hi everyone here's our next question. CPG islands are associated with which of the following. And our answer choices are assimilation. The assimilation methylation or di methylation and our answer choice here is going to be choice C. Methylation. A. Methylation is the addition of a methyl group and This most often occurs at position five of the base side is seen. So obviously when you have the C. G. Rich the CG islands um that's going to be a place of more methylation because of the prevalence of cytosine and in addition um that tends to be concentrated even particularly in C. G double. It's when they occur together. So rather than randomly occurring throughout the genome method. Areas of methylation tend to be occur in these concentrated CG islands and they're often located near promoters. Since methylation is really important and epigenetic modification that affects the transcription levels of different genes. So let's look at our other answer choices here. Um Joyce di di methylation obviously di methylation will occur where there were methyl groups originally on the D. N. A. But it's not specifically wouldn't think of it as associated with the CPG island. It just occurs um When you either have passive prevention of the addition of a methyl group in replicating cells or you have active removal by enzymes of those methyl groups. So that's why that's not our answer choice then. Choice A. And B. A. Is a sad elation. B. D. Assimilation. Um These are not associated with CPG islands. These are associated with his stones. This is another epigenetic modification. A circulation of his stones changes the chroma tin architecture by opening or closing the chromosome structure. Um, when chroma tin is very condensed, those jeans don't get expressed. So assimilation, assimilation causes genes to be expressed or not expressed based on the architecture of the crow maten. But again, those processes are having to do with his stones, not with these, not with cytosine bases or CG islands, so that's why that's not our correct answer. So again, CPG islands are associated with which the following choice C methylation. See you in the next video.