Activation and inactivation of Pseudomonas stutzeri methylbenzene catabolism pathways mediated by a transposable element

The arrangement of the genes involved in o-xylene, m-xylene, and p-xylene c atabolism was investigated in three Pseudomonas stutzeri strains: the wild- type strain OX1, which is able to grow on o-xylene but not on the meta and para isomers; the mutant M1, which grows on m-xylene and p-xylene but is un able to utilize the ortho isomer; and the revertant R1, which can utilize a ll the three isomers of xylene, A 3-kb insertion sequence (IS) termed ISPs1 , which inactivates the m-xylene and p-xylene catabolic pathway in P. stutz eri OX1 and the o-xylene catabolic genes in P. stutzeri M1, was detected. N o IS was detected in the corresponding catabolic regions of the P, stutzeri R1 genome. ISPs1 is present in several copies in the genomes of the three strains. It is flanked by 24-bp imperfect inverted repeats, causes the dire ct duplication of 8 bp in the target DNA, and seems to be related to the IS L3 family.