Humans have up to 25,000 protein-coding genes. DNA methylation, which occurs when methyl groups are added to DNA, plays a crucial role in which genes get turned on or off. Methyl groups alter a chromosome, but not the DNA sequence itself. For decades, scientists thought a methyl group could bond only to cytosine—one of DNA’s four bases.
Andrew Xiao, Ph.D., associate professor of genetics, and his team reported in Nature that methylation occurs on another DNA base: adenine. Xiao investigated how this methyl bond interacts with a specific transposon, which is an ancient virus that invaded our genome long ago and now serves to control gene expression, especially on X chromosomes.
“We know transposons are helpful because they can freely jump to different parts of the chromosome, thus allowing our DNA to modify to different environmental factors,” Xiao said. Since these transposons are also found in cancer cells, perhaps this type of DNA methylation could be a target for cancer, Xiao said.