Mureidomycins (MRDs) were isolated from Streptomyces flavidoviridens SANK60486 (10-13). They are active against Pseudomonas strains and protected mice against P. aeruginosa infection. MRDs A – D are uridylpeptide natural products containing a 3-deoxyuridine sugar attached via an enamide linkage to a peptide chain. MRDs C and D contain an additional glycine residue at the amino terminus, while B and D contain dihydrouracil in place of uracil. MRD A selectively inhibits bacterial MraY translocase, showing no inhibition of bacterial teichoic acid or mammalian glycoprotein biosynthesis. MRD A showed time-dependent inhibition of solubilised E. coli translocase I, and was found to be a slow-binding inhibitor. Closely related to the MRDs are the pacidamycins (PACs) (2, 4, 15) and napsamycins (NPSs) (1). Both have similar activities against Pseudomonas sp., but did not protect mice against P. aeruginosa infection.