Molecular biology - New tool for genome surgery

Gene therapy is the holy grail of human medicine. Many diseases are caused by a defective gene, sometimes with a mutation as subtle as a single-nucleotide variation. Before restoration of such a mutation in a patient's genome can take place, the target nucleotide sequence has to be cleaved at a single position, out of 3 billion possibilities. This degree of precise surgery requires an enzyme with highly selective target recognition. Successful editing of eukaryotic genomes has been accomplished with DNA nucleases designed to bear a unique site that binds to a specific DNA sequence. A major drawback of these protein-guided systems to "engineer" genomes, however, is that each new target sequence requires laboriously adjusting the specificity of the nuclease's DNA binding site. On pages 819 and 823 of this issue, Cong et al. (1) and Mali et al. (2) describe efficient genome editing in human cells based on an RNA-guided system