Genes specifying degradation of 3-chlorobenzoic acid in plasmids pAC27 and pJP4

All of the structural genes for 3-chlorobenzoate degradation are clustered in a 4.2-kilobase (kb) region of plasmid pAC25 (or pAC27) in Pseudomonas putida. An approximate 10-kb DNA segment containing three structural genes for chlorocatechol metabolism present on plasmid pJP4 in Alcaligenes eutrophus shows homology with the above 4.2-kb region of pAC27. In spite of the detectable sequence homology in the structural genes present on both plasmids, the regulation of their expression seems quite different; unlike pAC27, structural rearrangements are prerequisite for efficient expression of the 3-chlorobenzoate genes on plasmid pJP4. Structural features such as stem-loop structures present on plasmid pJP4 are most likely the starting materials for such rearrangements.