29 April 2005
Vol 308, Issue 5722

About The Cover

Cover image expansion

COVER A ring of 40 helices (yellow) forms the rotor of a bacterial enzyme that cleaves adenosine triphosphate (ATP). See page 654. The rotor is part of a mechanism for transporting sodium ions (red spheres) out of the cell. In eukaryotes, similar rotors generate ion gradients for protein trafficking, endocytosis, and neurotransmitter release, and they help to make ATP. [Image: M. G. Montgomery]