FEN1 Protein with DNA Strand (IMAGE) DOE/Lawrence Berkeley National Laboratory Caption Shown is the crystal structure of the FEN1 protein bound to its target DNA. Researchers found that single-stranded flaps are threaded through a tunnel in FEN1. The unexpected inversion of the threaded flap, guided by phosphate steering, keeps the phosphodiester bonds facing away from the metals that could inadvertently shred them. Credit Susan Tsutakawa/Berkeley Lab Usage Restrictions Editorial use only. 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.