Decoding the genome's `stickiest' parts

The complicated puzzle that is the human genome is almost completely decoded -- and Wistar Institute researcher Harold Riethman has played a large role in understanding a segment of it. Riethman and his team, which included scientists from the University of California at Irvine, sequenced 34 of 46 telomeres -- the sections of DNA that are found at the ends of the 23 chromosomes contained in human cells. Their work appears in this week's edition of the journal Nature. "[Telomeres] are kind of sticky," said Carol Ezzell, an editor of Scientific American. "They are difficult to do sequencing on." But Riethman focused his research on those "sticky" telomeres -- which can be compared to the plastic tips on the ends of shoelaces that prevent the laces from becoming unraveled -- to discover the boundaries which limit the mapping of the human genome. "There's no way to gauge how much is left, how much is complete," Riethman said of the current gene map, which was unveiled Monday in Washington by the Human Genome Project. "[Telomeric sequencing] provides some insurance that most or all of the DNA is contained in the sequence itself." Sequencing is the process of reading the strings of over three million bases -- chemical compounds referred to by the letters A, C, T and G -- which make up DNA. The bases code for genes much like letters make up words. The 30,000 or so genes then direct the production of proteins that determine everything from the color of our eyes to our susceptibility to disease. The map produced by the Human Genome Project, an initiative jointly run by the National Institutes of Health and the U.S. Department of Energy, covers only 96 percent of the genome. Much of the data contained in the genome represents relics from human beings' evolutionary ancestors. "The book of life is actually at least three books," said Director of the National Human Genome Research Institute Francis Collins at the press conference in Washington. One of the books Collins referred to is "a history book -- a narrative of the journey of our species through time." Riethman said that his work may provide answers to questions such as "how different ethnic groups are related and how humans are related to other species." "Segments of DNA adjacent to the very tip of chromosomes can be species-specific," Riethman said. But answers to those questions are at least a few years off. "We still have a lot of gaps," Riethman said, pointing out that sequencing is only the first step in decoding the function of the genes the telomeric regions encode. "For the next two or three years we're going to focus intensively to get those [gaps] closed up." "The next step," Riethman added, "is to analyze the large segments [of DNA] that are either present or absent in different segments of the human population." "It's as though we have climbed to the top of the Himalayas," Director of the Whitehead Institute Center for Genome Research Eric Lander said of the Human Genome Project in a statement. "For many years to come, we will be exploring the intricate details of the terrain ahead." "We've got a long way to go before we will ultimately understand all the secrets that the genome has to tell us," Lander added.