Contents

22 December 1989
Vol 246, Issue 4937

About The Cover

Eighteen of 1989's top scientific achievements are discussed in a year-end wrap-up, and from this group the “Molecule of the Year” was chosen. The winner—an enzyme that drives a cyclic amplification reaction that produces millions of copies of interesting genes and gene segments. See page 1541 and 1543. [Image by Lewis E. Calver, courtesy of Cetus Corporation, Emeryville, CA 94608]