<jats:p>A <jats:italic>Streptomyces clavuligerus</jats:italic> gene (designated <jats:italic>claR</jats:italic> ) located downstream from the gene encoding clavaminate synthase in the clavulanic acid biosynthetic gene cluster is involved in regulation of the late steps in clavulanic acid biosynthesis. Nucleotide sequence analysis and database searching of ClaR identified a significant similarity to the helix–turn–helix motif (HTH) region of LysR transcriptional regulators. A gene replacement mutant disrupted in <jats:italic>claR</jats:italic> was unable to produce clavulanic acid, suggesting that <jats:italic>claR</jats:italic> is essential for clavulanic acid biosynthesis. Furthermore, the accumulation of clavaminic acid in the <jats:italic>claR</jats:italic> mutant suggested that ClaR regulates the late steps in the clavulanic acid pathway, i.e. those involved in the conversion of clavaminic acid to clavulanic acid. Transcriptional analysis using RNA isolated from the wild type and the <jats:italic>claR</jats:italic> mutant showed that the expression of the putative late genes, but not the early genes, was regulated by ClaR. High‐resolution S1 nuclease analysis of <jats:italic>claR</jats:italic> suggested that it is expressed as a monocistronic transcript and also as a bicistronic transcript along with the late gene <jats:italic>orf‐9</jats:italic>. The transcription start site of the monocistronic <jats:italic>claR</jats:italic> transcript was identified as a C residue 155 nucleotides upstream from the <jats:italic>claR</jats:italic> start codon.