The TTA codon-containing adpA gene of Streptomyces clavuligerus, located upstream of ornA, is in a DNA region syntenous with the homologous region of other Streptomyces genomes. Deletion of adpA results in a medium-dependent sparse aerial mycelium formation and lack of sporulation. Clavulanic acid formation in this mutant decreases to about 10 % of the wild-type level depending on the medium, whereas its production is strongly stimulated by increasing the adpA copy number. Quantitative transcriptional analysis indicates that expression of the clavulanic acid regulatory genes ccaR and claR decreases seven- and fourfold, respectively, in the DeltaadpA mutant, resulting in a large decrease in expression of genes encoding biosynthesis enzymes for the early steps of clavulanic acid formation and a smaller decrease in the expression of genes for the late steps of the pathway. An ARE box, 5'-TCTCATGGAGACATAGCGGGGCATGC-3', is present upstream of adpA and efficiently binds S. clavuligerus Brp protein, as shown by electrophoretic mobility shift assay (EMSA) analysis. The transcription level of adpA is higher in the absence of Brp, as shown in S. clavuligerus Deltabrp, suggesting a connection between adpA expression and the gamma-butyrolactone system in S. clavuligerus.