A 5.8-kb segment from the upstream region of the cholesterol oxidase (choA)-Cytochrome P450 (choP) operon of Streptomyces sp. SA-COO was sequenced. Computer assisted analysis of the sequence revealed four open reading frames (ORFs), whose deduced gene products could be classified into two groups. Cho-Orfl, the C-terminal segment of Cho-Orf3, and Cho-Orf4 were homologous to each other and showed similarities to the DNA-binding domains of bacterial response regulators of the UhpA subfamily, while a putative transmembrane protein, Cho-Orf2, and the N-terminal segment of Cho-Orf3 were homologous to each other but no homologies to known proteins were found. The genes coding for these putative proteins appeared to be organized as repeating units. Structural features of the nucleotide sequence and the homologies of the predicted gene products are discussed.