28 April 2000
Vol 288, Issue 5466

About The Cover

Cover image expansion

COVER Two views of a backbone model of RNA polymerase II, the central enzyme of gene expression, derived from x-ray crystallography. DNA, depicted as a blue helix, was placed in the structure on the basis of results from electron crystallography. The direction of transcription is from right to left in the view at the upper left and from back to front in the view at the lower right. A pink sphere identifies a metal ion at the active center. See page 640 [Image: P. Cramer et al.]