Chapter 17, Problem 26ESP

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?