Scientists have taken the first steps toward writing the blueprint of life in an alphabet unknown to nature, they reported online in the journal Nature. Until now, biologists who synthesise DNA in the lab have used the same molecules — called bases — that are found in nature. But Floyd Romesberg of the Scripps Research Institute in La Jolla, California, and colleagues not only created two new bases, but also inserted them into a single-cell organism and found that the invented bases replicate like natural DNA, though more slowly. The scientists reported that they got the organisms, the common bacteria E coli, to replicate about 24 times over the course of 15 hours. The accomplishment “redefines this fundamental feature of life”, wrote biologists Ross Thyer and Jared Ellefson of the University of Texas, Austin, in a commentary in Nature on Wednesday.