ssDNA and the Argonautes: The Quest for the Next Golden Editor.

Genome engineering has gone mainstream because of breakthroughs in defining and harnessing naturally occurring, customizable DNA recognition cursors (protein or RNA-guided). At present, most gene editing relies on these cursors to direct custom DNA endonucleases to a specific genomic sequence to induce a double-strand break. New tools for genome engineering are continuously being explored, and another advance in DNA targeting has recently been described. Argonaute isolated from Natronobacterium gregoryi (NgAgo) is an ssDNA-based cursor that thus far has no known limitations in sequence recognition, shows promise for high specificity, and for many applications may represent a potentially more accessible genome-editing system over prior tools as it requires only a single, 24-base, 5' phosphorylated ssDNA for DNA targeting. Genome engineering is in a remarkable moment of unprecedented growth with exponential reduction in costs reminiscent of Moore's law in electronics. Many questions remain with regard to Argonaute utility in specific systems, but there is no doubt that genome engineering is expanding into new and exciting areas from synthetic biology to gene therapy.