Contents

10 December 1993
Vol 262, Issue 5140

About The Cover

Two-dimensional agarose gel electrophoresis of replicating DNA reveals the locations of DNA replication origins. DNA fragments are separated on the basis of mass (from left to right) and shape (from top to bottom). In this artificially colorized autoradiogram, a yeast chromosomal replication origin is detected first as a series of fragments that contain bubbles (right arc) and later as a series of large simple Y's (left vertical arc). See page 1728. [Autoradiogram: Bonita J. Brewer. Colorization: Walton L. Fangman]