The argG gene of Streptomyces clavuligerus (Scl) has been cloned by complementation of argG mutants of Escherichia coli and S. lividans (Sl). The argG nucleotide (nt) sequence showed that it corresponds to a new type of argG different from the corresponding genes of S. coelicolor (Sco) and Sl. It encodes a 43,250-Da protein that showed higher similarity to argininosuccinate synthetases (ASS) from Methanococcus vannielii and Methanosarcina barkeri than to ASS deduced from other Streptomyces argG. No hybridization of the Scl argG was found with the homologous genes of Sl or Sco. The argH gene was located downstream from argG in Scl. The genomic region around argG and argH in Scl was different from the homologous regions in other Streptomyces and is not genetically unstable, unlike in Sco and Sl. Amplification of argG in transformant Scl[pULAR113] results in a 2.3-fold increase in the production of clavulanic acid (CA) in relation to the control strain Scl[pIJ699].