Junk genes

An ancient Chinese legend tells the story of the daughter of the country’s first emperor: After drowning in the East China Sea, Jingwei was reincarnated as a beautiful bird who flew about dropping stones and wood to fill in the sea, hoping to save others from a similar fate.

Today, Jingwei has been reborn again, this time as a fruit-fly gene discovered by Manyuan Long, assistant professor in ecology & evolution: “We used the name jingwei because this gene avoided the usual fate of the processed [useless] gene—death—and was ‘reincarnated’ into a new structure with a novel function.”

Long’s discovery of jingwei in 1993, when he was a doctoral student at the University of California, Davis—along with his other contributions to genetics—led to his selection this fall as one of 24 David and Lucile Packard fellows in science and engineering. The national fellowships provide $625,000 over five years to help support young researchers’ work in chemistry, biology, physics, mathematics, astronomy, and computer science.

Focusing on how human genes evolve, Long uses molecular techniques and computer software to search for new genes and to compare and contrast thousands of genes at a time. He is particularly intrigued by the creation of new genes through the naturally occurring shuffling and mixing of gene fragments. As he explains, so-called junk DNA, or introns—stretches of genetic material that appear to have no real function—actually allow gene fragments to recombine and create new genes without overlapping. Long plans to use the grant to learn more about jingwei’s function and its creation through gene shuffling.

He also wants to prove the so-called “introns-early” theory. Proposed by Walter Gilbert, Long’s postdoctoral adviser at Harvard, the theory suggests that introns existed two billion years ago, before bacteria diverged from plant and animal cells. Because bacteria do not contain introns, some evolutionary biologists believe introns developed after the divergence of these early life forms—the “introns-late” theory. Long maintains that bacteria once had introns but lost them to facilitate faster replication. Smaller organisms, like bacteria, he says, need to replicate quickly to respond to environmental stresses, while larger organisms, which rely less on rapid replication to survive changes in the environment, can accumulate more introns over time. If bacterial cells, which replicate as fast as once every 30 minutes, had to copy long stretches of useless DNA every time they divided, he notes, their growth rate could be nowhere near as rapid.

In a related study, Long is looking at whether organisms with larger genomes have more of their genetic material devoted to introns.—Sharon Parmet