Mapping a clan of mobile selfish genes( Much of human DNA is the genetic equ...)

Much of human DNA is the genetic equivalent of e-mail spam: short repeated sequences that have no obvious function other than making more of themselves.

After starting out in our primate ancestors 65 million years ago, one type of repetitive DNA called an Alu retrotransposon now takes up 10 percent of our genome, with about one million copies. Roughly every 20th newborn baby has a new Alu retrotransposon somewhere in its DNA, scientists have estimated.

"I think of them as molecular machines that can copy themselves and move around the genome, says Scott Devine, PhD, assistant professor of biochemistry at Emory University School of Medicine. "These elements pose a major threat to our genetic information, because they can damage genes when they jump into them, leading to altered traits or diseases such as cancers."

As mutations gradually blur the features of older Alu elements, some become unable to make copies of themselves. To identify the Alu retrotransposons that are still capable of moving around, Devine and graduate student E. Andrew Bennett, who is first author, divided them into families and tested a representative of each family in the laboratory.

The results are published online and are scheduled to appear in the December issue of the journal Genome Research. Laboratories at Emory, the University of Michigan and the Max Planck Institute for Developmental Biology contributed to the study.

"We wanted to see what dictates whether an Alu element will be mobile," Devine says. "That way we could predict which Alu copies are more likely to damage our genetic information. This information will become very useful as we enter the age of personalized genomics, allowing us to make predictions about the future health of individuals."

Alu elements get their name because they usually include the recognition site for the enzyme Alu I (AGCT), a common laboratory tool for cutting DNA into pieces. Geneticists
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