Using a new method to catch elusive "jumping genes" in the act, researchers have found two human proteins that are used by one type of DNA to replicate itself and move from place to place. The discovery, described in the Nov. 21 issue of Cell, breaks new ground, they say, in understanding the arms race between a jumping gene driven to colonize new areas of the human genome and cells working to limit the risk posed by such volatile bits of DNA.
Jumping genes, more formally known as transposons or transposable elements, are DNA segments with the blueprints for proteins that help to either copy the segment or remove it, then insert it into a new place in the genome. Human genomes are littered with the remnants of ancient jumping genes, but because cells have an interest in limiting such trespasses, they have evolved ways to regulate them. Most jumping genes have mutated and can no longer move, but these "rusting hulks" are still passed down from generation to generation.
One exception is a jumping gene called L1, which has been so successful that copies of it make up about 20 percent of human DNA. While many of these copies are now mutated and dormant, others are still active and thus the subject of much interest from geneticists.
"Human cells have evolved ways of limiting jumping genes' activity, since the more frequently they move, the more likely they are to disrupt an important gene and cause serious damage," says Lixin Dai, Ph.D., a postdoctoral associate at the Johns Hopkins Institute for Basic Biomedical Sciences, who led the study. To find out more about how cells control L1 and what tricks the jumping gene uses to get around these defenses, Dai and others in the laboratory of Jef Boeke, Ph.D., first induced lab-grown human cells to make large amounts of the proteins for which L1 contains the blueprints. As expected, the two types of L1 protein joined with human proteins and genetic material called RNA to form so-call
|Contact: Shawna Williams|
Johns Hopkins Medicine