The cover shows a ribbon diagram representation of E. coli RNase HI co-crystallized with two Mn2+ ions and solved at 1.9- resolution. The divalent metal ions are purple, active site carboxylates are shown in green, and metal-coordinating oxygens and water molecules are in red. The position of these two ions is consistent with the activation/attenuation model for RNase H activity. Details can found in the article by Goedken and Marqusee, pages 7266-7271.7266.