12 May 2000
Vol 288, Issue 5468

About The Cover

Cover image expansion

COVER Sculpture representing the mechanics of the mammalian circadian clock. Two brass pulleys with oppositely positioned short hands (representing 24-hour positive and negative feedback loops) are belt-driven by the small pulley (transcriptional machinery). The belt connecting the two "loops" also moves the center pulley and its large hand, generating an output rhythm. See page 1013 [Sculpture: Jason S. Reppert; photo: Samuel C. Riley; photo illustration: C. Faber Smith]