Contents

26 March 1993
Vol 259, Issue 5103

About The Cover

Transparent surface models of the helical nucleoprotein filaments formed by the yeast RAD51 protein (top) and the bacterial RecA protein (bottom). Within RAD51 filaments, DNA (red) is extended and untwisted in a manner similar to its extension and untwisting in RecA filaments. The homology of these filaments suggests that the structures for recombination in eukaryotes are similar to those in prokaryotes. See page 1896. [Computer graphic: Edward H. Egelman]