ProCas9 Sensor (IMAGE) University of California - Berkeley Caption ProCas9 can sense the presence of an enzyme called a protease. ProCas9 (left, gray) is inactive until the protease snips a short piece of protein (red loop), at which point it becomes active (right, red) and binds DNA. By making the Cas9 fluoresce when it binds DNA, researchers get a signal that the protease is present. Credit UC Berkeley Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.