Ubiquitin Superposed (IMAGE) Goethe University Frankfurt Caption Superposed crystal structures of ubiquitin (green) and ubiquitin modified by the Legionella enzyme (yellow). Modified ubiquitin contains an additional phosphoribosyl group at amino acid position 42. Credit <i>Cell</i> 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.