Scientists have created the first organism with synthetic DNA that can replicate in a cell, an achievement that promises to add new letters to the genetic code underlying life on earth.

In the natural world, just two chemical base pairs, known simply as A-T and C-G, constitute the building blocks of DNA in all life forms. Research published yesterday in the journal Nature describes the creation of a cell that contains a man-made base pair, dubbed d5SICS-dNAM.

By expanding the natural boundaries of what constitutes life, scientists hope they can one day create new proteins that can handle a variety of chores in the body, potentially leading to unique ways to attack disease. The approach is safe, the researchers said, because it includes a chemical additive that the cell needs to survive.

We created an organism that lives and stably harbors genetic information in its DNA, said Floyd Romesberg, a chemist at La Jolla, California-based Scripps Research Institute, whose laboratory created the new organism. Instead of two base pairs, it has a third.

All life on earth is based on the combination of four chemicals. Adenine bonds naturally with thymine to create the A-T section of the formula, while guanine and cytosine make up the C-G part. The joining of these base pairs in different combinations creates amino acids and proteins that power life.

Romesbergs work differs from other research in the field of genetic engineering in that it involves creation of components that are purely synthetic and integrated into the machinery of life in a cell, he said in a telephone interview.

Other scientists in the field, notably J. Craig Venter, work by constructing genetic material from natural building blocks, or natural components of DNA and proteins.

Starting in 2009, Romesberg and his laboratory created about 300 nucleotides with the newly constituted DNA before landing on ones they believed might be able to replicate in a cell. They then used a special chemical transporter to get the synthetic base pair into an E.coli cell, where it replicated without affecting cell growth. That suggests it wasnt recognized as atypical by the bodys natural DNA repair machinery, according to the paper.

Synthorx Inc., a San Diego-based biotechnology company, has exclusive rights to the synthetic biology from Scripps. The company plans to focus on developing the technology for use in vaccines, medicines and diagnostics, the company said yesterday in a statement.

The research, though promising for fields of medicine and drug development, will probably raise ethical and safety concerns, said Arthur Caplan, head of the division of bioethics at NYU Langone Medical School. He called the research promising.

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Scientists Add New Letters to Lifes Genetic Alphabet