DURHAM, N.C. -- Duke University Medical Center biochemists have made the startling discovery that an enzyme that copies DNA in living cells can also be made to operate when held in place in crystal form.
Their achievement opens the way for understanding the finest details of how the intricate DNA-copying enzyme -- called DNA polymerase -- manages to reproduce DNA with the impeccable accuracy necessary for all living things to grow and reproduce nearly flawlessly.
By shining X-rays through the actively functioning crystals, the biochemists have taken snapshots that catch the enzyme in the biochemical act of copying DNA. Soon they will make movies. The scientists' images also are revealing details of how cancer-causing chemicals interfere with the copying process.
The biochemists, led by assistant professor of biochemistry Lorena Beese, published their discovery in the Jan. 15 issue of Nature, in an article titled "Visualizing DNA Replication in a Catalytically Active Polymerase at 1.8 Angstrom Resolution." Besides Beese, authors of the paper are graduate student James Kiefer and postdoctoral associate Chen Mao of Duke, and researcher Jeffrey Braman of Stratagene of La Jolla, Calif.
The scientists' work was supported by the American Cancer Society, the Searle Scholar Foundation, and the North Carolina Biotechnology Center.
Enzymes are proteins that are the workhorses of the cell, catalyzing the multitude of chemical reactions that underlie all cell functions. The molecules that enzymes act upon are called substrates.
The DNA polymerase that the Duke researchers studied is part of a
complex molecular assembly line that is central to all cell division. A cell
preparing to divide first unzips its double-stranded DNA into a single strand,
to prepare for DNA copying. DNA polymerase then attaches to one strand, using it
as a template. The polymerase works its way along the strand, chemical
Contact: Dennis Meredith