Many genes that exist naturally in the body turn on and off when needed; otherwise they would crank out superfluous proteins nonstop. But the artificial genes that are injected to treat disease generally are simpler constructs and are always “on,” starting protein production soon after they reach the bloodstream. Now, researchers at SRI International in Menlo Park, CA, have constructed an artificial gene with an “off” switch.SRI’s experimental gene directs the production of proteins responsible for growing new blood vessels. Persistent low levels of oxygen in cardiac muscle-often an early warning of clogged blood vessels that can cause heart attack-turn the gene on, initiating the production of blood vessels. Over time, these new vessels remedy the oxygen shortage. When the oxygen level returns to normal, the gene switches “off.” SRI has secured two patents on the unique DNA sequence that acts as the gene’s switch.