Researchers create new rung on DNA ladder, offering hope of new drugs

For billions of years, the DNA blueprints for life on earth have been written with just four genetic "letters" - A, T, G and C.

On Wednesday, scientists announced that that they added two more.

In a paper published in the journal Nature, bioengineers at Scripps Research Institute in San Diego, California, said they had inserted two synthetic molecules into the genome of an Escherichia coli bacterium, which survived and passed on the new genetic material to its offspring.

In addition to the naturally occurring nucleotides adenine, thymine, guanine and cytosine, which form the rungs of DNA's double-helix structure, the bacterium carried two more base-pair partners.

For more than a decade, scientists have been experimenting with so-called unnatural base pairs, or UBPs, saying they may hold the key to new antibiotics, future cancer drugs, improved vaccines, nanomaterials and other innovations. Until now, however, those experiments have all been conducted in test tubes.

"These unnatural base pairs have worked beautifully in vitro, but the big challenge has been to get them working in the much more complex environment of a living cell," lead study author Denis Malyshev, a molecular and chemical biologist at Scripps, said.

The new genetic material did not appear to be toxic to the bacteria, and it only remains in the organism's genome under specific lab conditions. In a natural environment, the molecules - nucleoside triphosphates - degrade and disappear in a day or two. Once they disappear, the bacterium reverts back to its natural base pair arrangement.