Hutchison, C.A. et al. Science 351, 1414 (2016).

The goal of Hutchison et al. at the J. Craig Venter Institute is easily described: to build a viable cell so simple that the function of every gene can be defined. The researchers started with the 1,079-kb genome of Mycoplasma mycoides, which they had completely synthesized in 2010, and deleted genes deemed non-essential on the basis of mutagenesis experiments and current knowledge of molecular biology. The initial design failed, but a refined mutagenesis strategy and retention of quasi-essential genes, needed for robust growth, resulted in a viable JCVI-syn3.0 with a 531-kb genome encoding 438 proteins and 35 RNAs. Of these 473 genes, the function of 149 is still unknown, but the design principles developed in this work will allow further testing and the design of more genomes.