These steps are chemically interesting, but the mystery that compelled the scientists at the Frontiers symposium surrounds the initial transcript that is created by a species of ribonucleic acid called messenger RNA (mRNA). Tjian's overview, "Gene Regulation in Animal Cells: Transcription Factors and Mechanisms," touched on much of the above background and presented some of the basic issues scientists are exploring as they probe the mRNA process. His colleagues in the session on gene regulation each described intriguing findings based on their studies of regulation in various organisms: Arnold Berk, from the University of California, Los Angeles, in viruses; Kevin Struhl, from the Harvard Medical School, in yeast; Ruth Lehmann, from the Whitehead Institute, in the fruit fly; and Hanahan, in mice. They explained their work to the symposium and suggested how its implications may help to clarify human genetics and fill in the larger picture of how life operates.

THE ROLE OF DNA

Noncoding DNA—Subtlety, Punctuation, or Just Plain Junk?

Scientists cannot say for certain whether the majority of noncoding genes that do not seem to say simply "make this string of amino acids," are saying anything at all. Tjian has heard a lot of speculation on this question: "Most people in the field agree that only a very small percentage of the human genome is actually coding for . . . the proteins that actually do all the hard work. But far be it for me to say that all that intervening sequence is entirely unimportant. The fact is we don't know what they do." He notes an interesting phenomenon among scientists, observing that while "some people call it junk," others like himself ''would rather say 'I don't know.''' Rather than dismissing the significance of this undeciphered DNA, he and others mentally classify it as Punctuation that is modifying and influencing the transcript. "There is clearly a lot of punctuation going on, yet still the question arises: Why do amphibians have so much more DNA than we do? Why does the simple lily have so much DNA, while the human—clearly just as complicated in terms of metabolic processes—doesn't seem to need it? Actually, a lot of people wonder about whether those sequences are perhaps there for more subtle differences—differences between you and me that at our present stage of sophistication may be too difficult to discern."

Eric Lander, responding to the curiosity about excess or junk genes, pointed out that the question often posed is, If it is not useful, why is it there? He continued, "From an evolutionary point of view, of



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