The cytochrome P-450cam hydroxylase operon of Pseudomonas putida PpG1 (ATCC 17543) encodes proteins responsible for early steps of the degradation of D-camphor. Transcription of this operon is negatively controlled by the cam repressor (CamR), and the expression of camR is autoregulated. CamR was purified from Escherichia coli harboring an overproducing plasmid. The repressor forms a homodimer with a molecular mass of 40 kDa, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and gel filtration. CamR protected a specific DNA region from attack by DNase I. This region contains a palindromic operator of the cytochrome P-450cam hydroxylase operon and of the camR gene. Protection was inhibited by the addition of 60 microM D-camphor and also by certain camphor analogs and degradation products, including D-3-bromocamphor, adamantane, 2-adamantanone, 5-exo-hydroxycamphor, and 2,5-diketocamphane. These analogs and degradation products induced cytochrome P-450cam hydroxylase operon expression in vivo.