Tubes of <i>E. coli </i> (IMAGE) Proceedings of the National Academy of Sciences Caption These are tubes of E. coli bacterial culture genetically engineered to fluoresce upon retrotransposition of the human retroelement LINE-1. The tube on the right has had expression of LINE-1 turned on, while the tube on the left has not. Credit Thomas E. Kuhlman 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.