Cover photograph (Copyright © 2000, American Society for Microbiology. All rights reserved.): Three representations of the amino acid L-tryptophan: a largely insubstantial wire frame, a stick model, and a detailed space-filling model. Work on the regulation of the synthesis of this amino acid similarly went from intriguing clues to detailed mechanistic models of the sequential events that contribute to the process of transcriptional attenuation. (See related article on page 1.)