Cover photograph (Copyright © 2001, American Society for Microbiology. All rights reserved.): Acetate kinase, a shadow of the past. Determination of the structure of acetate kinase suggests that it may be an early member of the ASKHA (acetate and sugar kinase, Hsp70, and actin) family. This enzyme is central to interspecies and interdomain metabolic cooperation. The protein portrait was made by using the programs povscript (Daniel Peisach, peisach{at}umich.edu), molscript (Per Kraulis, www.avatar.se/molscript), and povray (www.povray.org). (See related article on page 680.)