Coronafacic acid (CFA), the polyketide component of the phytotoxin coronatine (COR), is activated and coupled to coronamic acid via amide bond formation, a biosynthetic step presumably catalyzed by the CFA ligase (cfl) gene product. The COR biosynthetic gene cluster in Pseudomonas syringae pv. glycinea PG4180 is located within a 32-kb region of a 90-kb plasmid designated p4180A. In the present study, a cloned region of p4180A complemented all CFA2 mutants spanning an 18.8-kb region of the COR biosynthetic cluster. The genetic evidence presented in this study indicates that cfl and the CFA biosynthetic gene cluster are encoded by a single transcript and that transcription of all of the genes in this operon is directed by the cfl promoter. The cfl promoter was localized to a 0.37-kb region upstream of the transcriptional start site by progressive subcloning in pRG960sd, a vector containing a promoterless glucuronidase gene. Transcription of the cfl/CFA operon was temperature sensitive and showed maximal glucuronidase activity at 18&C. Furthermore, transcription of the cfl/CFA operon was dependent on the functional activity of a modified two-component regulatory system located within the COR biosynthetic gene cluster. Thermoregulation of the cfl/CFA operon and the coronamic acid biosynthetic gene cluster via the modified two-component regulatory system is discussed.