orf7 (oppA1) and orf15 (oppA2) are located 8 kb apart in the clavulanic acid gene cluster of Streptomyces clavuligerus and encode proteins which are 48.0% identical. These proteins show sequence similarity to periplasmic oligopeptide-binding proteins. Mutant S. clavuligerus oppA1::acc, disrupted in oppA1, lacks clavulanic acid production. Clavulanic acid production is restored by transformation with plasmid pIJ699-oppA1, which carries oppA1, but not with the multicopy plasmid pIJ699-oppA2, which carries oppA2. The mutant S. clavuligerus oppA2::aph also lacks clavulanic acid production, shows a bald phenotype, and overproduces holomycin (5). Clavulanic acid production at low levels is restored in the oppA2-disrupted mutants by transformation with plasmid pIJ699-oppA2, but it is not complemented by the multicopy plasmid pIJ699-oppA1. Both genes encode oligopeptide permeases with different substrate specificities. The disrupted S. clavuligerus oppA2::aph is not able to grow on RPPGFSPFR (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg; bradykinin), but both mutants grow on VAPG (Val-Ala-Pro-Gly) as the only nitrogen source, indicating differences in the peptide bound by the proteins encoded by both genes. The null S. clavuligerus oppA1::acc and S. clavuligerus oppA2::aph mutants are more resistant to the toxic tripeptide phosphinothricyl-alanyl-alanine (also named bialaphos) than the wild-type strain, suggesting that this peptide might be transported by these peptide-binding proteins.