08 June 2001
Vol 292, Issue 5523

About The Cover

Cover image expansion

COVER The enzyme RNA polymerase II in the act of transcribing a gene. X-ray crystal structure comprises the protein (gray, except for orange "clamp" and green "bridge" helix), DNA (blue template strand, green nontemplate strand), and RNA (red). The pink sphere is an active center Mg2+ ion. Double-stranded DNA enters from the right and unwinds before the active center. The unwound nontemplate DNA strand is obscured by motion or disorder. 1876 [Adapted from Fig. 2C of Gnatt et al.]