The atuR-atuABCDEFGH gene cluster is essential for acyclic terpene utilization (Atu) in Pseudomonas aeruginosa and Pseudomonas citronellolis. The cluster encodes most proteins of the Atu pathway including the key enzyme, geranyl-CoA carboxylase. AtuR was identified as a repressor of the atu gene cluster expression by (1) amino acid similarity to TetR repressor family members, (2) constitutive expression of Atu proteins in the atuR insertion mutant and (3) specific binding of purified AtuR homodimers to the atuR-atuA intergenic region in electrophoretic mobility shift assay (EMSA). Two 13 bp inverted repeat sequences separated by 40 bp in the atuA operator/promoter region were identified to represent two sites of AtuR binding by EMSA. Changing of two or more bases within the inverted repeat sequences abolished the ability of AtuR to bind to its target. All EMSA experiments were sufficiently sensitive with ethidium bromide-stained DNA fragments after polyacrylamide gel electrophoresis.