A molecular tool borrowed from bacteria could provide a targeted way to switch genes on or off in human cells.

Species such as Streptococcus pyogenes can cleave DNA at specified sites using a protein called Cas9 and strands of RNA that guide Cas9 to its target. Jonathan Weissman of the University of California, San Francisco, and his colleagues have modified this system to control transcription — the production of a specified RNA from its DNA template.

Although many guide RNAs were ineffective, the system worked in yeast and human cells, in one case reducing expression of a targeted human gene by up to 80% with minimal effects on other genes. The method, called CRISPR interference after the bacterial system it involves, can silence a wider variety of sequences than the popular RNA-interference technique.

Cell http://dx.doi.org/10.1016/j.cell.2013.06.044 (2013)