G4 selection (IMAGE) Penn State Caption Illustration showing trends in the levels of purifying selection (purple) and thermostability (green) in G-quadruplexes (G4s)--sequences in the human genome that can fold into unusual three-dimensional structures--across different regions of the genome (shown at bottom). A new genome-wide study shows increased selection and stability of G4s in gene-regulatory regions and suggests that the unusual structures should be added to the list of functional elements in the genome. Credit Kateryna Makova and Dani Zemba, Penn State 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.