During cell division, DNA polymerase moves along the DNA molecule to faithfully replicate chromosomes at a rate of up to 400 building blocks (nucleotides) per second. The work shows in detail how the DNA polymerase recognizes the right nucleotide to be paired to the single-stranded DNA, and helps explain how this enzyme achieves its high accuracy of about one mistake per million bases. Scientists hope that the new structure will guide the development of better reagents for DNA sequencing - the greatest challenge in the Human Genome Project. The structure will also be of special interest to researchers developing drugs that target DNA replication. Many antiviral drugs, including the AIDS drug AZT and drugs against herpes simplex virus, inhibit DNA polymerase. For more information and photo of structure, see the Harvard Medical School press release announcing this achievement [URL not available] and the DOE Human Genome Program research abstract describing this work (http://www.ornl.gov/TechResources/Human_Genome/publicat/97santa/seqtech.html#24).