Cover photograph (Copyright © 2003, American Society for Microbiology. All Rights Reserved.): UDP-binding pocket of UDP-N-acetylmuramic acid:L-alanine ligase (MurC) from Haemophilus influenzae. MurC is the first of four related Mur ligases that add amino acids to the cytoplasmic precursor for the biosynthesis of bacterial cell wall peptidoglycan. Surprisingly, the manner in which the UDP of the substrate is recognized differs among these enzymes, with substantial diversity in the shapes and chemical environments of their UDP-binding pockets. Next-generation antimicrobial agents could be designed that mimic these enzyme-UDP interactions and independently target the individual enzymes of the cell wall biosynthesis pathway. Such antibacterial cocktails could effectively circumvent bacterial resistance mechanisms. (See related article on page 4152.)