Ever since Watson and Crick first cracked the structure of DNA in 1953, biochemists have speculated that hydrogen bonding between DNA's four bases plays a key role in the amazing accuracy of this genetic blueprint. But new research with a molecular imposter is calling some of these long-held beliefs into question. Results presented in the February 12 issue of the Journal of the American Chemical Society suggest strongly that the precision of DNA copying has much more to do with DNA's shape and the enzymes that copy it.
This finding brings into question decades of dogma on DNA replication, says researcher Eric Kool of the University of Rochester. Kool adds that the new information may help researchers develop new drugs that are better able to sneak in and kill sickly cells -- including deadly cancer cells.
Kool and co-workers created a ring-like molecule that very closely mimics the shape of the base thymine in DNA. This thymine mimic lacks the slightly charged regions needed to form hydrogen bonds with thymine's normal partner base, adenine. But when the mimic was placed into a strand of DNA, the scientists got a surprise: The cell's DNA-copying machinery correctly inserted adenine opposite the thymine-like base despite the absence of hydrogen bonds. Not only was adenine inserted opposite the thymine mimic, it was inserted correctly nearly all the time -- suggesting that base shape is more important than hydrogen bonds in ensuring accurate DNA replication.
"Most biochemistry textbooks cite hydrogen bonds as the primary reason that DNA is copied accurately," says Kool, a professor of chemistry. "Because of this finding, the next generation of texts may not be able to say that."
Hydrogen bonds form because of slight charge differences
between the atoms that make up adjacent molecules. Each of
the four DNA bases -- adenine, thymine, cytosine, and guanine --
has a characteristic arrangement of these partially
charged atoms that
Contact: Stephen Bradt
University of Rochester