CHARACTERIZATION OF THE EXPRESSION OF THE THCB GENE, CODING FOR A PESTICIDE-DEGRADING CYTOCHROME-P-450 IN RHODOCOCCUS STRAINS

A cytochrome P-450 system in Rhodococcus strains, encoded by thcB, thc C, and thcD, participates in the degradation of thiocarbamates and sev eral other pesticides, The regulation of the system was investigated b y fusing a truncated lacZ in frame to thcB, the structural gene for th e cytochrome P-450 monooxygenase, Analysis of the thcB-lacZ fusion sho wed that the expression of thcB was 10-fold higher in the presence of the herbicide EPTC (s-ethyl dipropylthiocarbamate). Similar enhancemen t of the thcB-lacZ expression was found with other thiocarbamate pesti cides, Atrazine, simazine, or carbofuran, although metabolized by the system, had no effect on the thcB-lacZ expression, The presence of glu cose slightly increased the expression of thcB-lacZ, indicating no cat abolic repression of the thcB-lacZ expression. The expression of thcB- lacZ was decreased more than twofold in Luria-Bertani medium. This was due in part to cysteine, which repressed thcB-lacZ expression, It was confirmed that the thcR gene, which is transcribed divergently from t hcB, codes for a positive regulatory protein which is essential for th e thcB-lacZ expression, Studies of the thcR-lacZ protein fusion showed that the thcR gene is expressed constitutively.