The Escherichia coli gene murZ was recently shown to encode UDP-N-acetylglucosamine enolpyruvyl transferase, which catalyzes the first committed step of peptidoglycan biosynthesis (J. L. Marquardt, D. A. Siegele, R. Kolter, and C. T. Walsh, J. Bacteriol. 174:5748-5752, 1992). The map position of murZ (69.3 min) differed from that determined for murA (90 min), a gene which had been previously proposed to encode the same activity (P.S. Venkateswaran and H. C. Wu, J. Bacteriol. 110:935-944, 1972). Here we describe the construction of a chromosomal deletion of murZ and a plasmid containing murZ under arabinose control. Growth of cells containing the murZ deletion was dependent on the expression of murZ from the plasmid. We conclude that murZ is an essential gene and encodes the sole UDP-N-acetylglucosamine enolpyruvyl transferase of E. coli. To simplify the nomenclature, we recommend that murA be used to designate the gene at 69.3 min that encodes this activity and that the designation murZ be abandoned.