Chapter 15, Problem 25PDQ

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 human cells. A bacterial gene, luciferase, was cloned next to eukaryotic promoter fragments that were methylated to various degrees, in vitro. The chimeric plasmids were then introduced into tissue culture cells, and the 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?

DNA Segment	Patch Size of Methylation (kb)	Number of Methylated CpGs	Relative Luciferase Expression
Outside transcription	0.0	0	490 $\times$
unit (0–7.6 kb away)	2.0	100	290 $\times$
	3.1	102	250 $\times$
	12.1	593	2 $\times$
Inside transcription unit	0.0	0	490 $\times$
	1.9	108	80 $\times$
	2.4	134	5 $\times$
	12.1	593	2 $\times$