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Research has been conducted on DEH transposon from Pseudomonas putida strain PP3. The function, the structure of this transposon and the full sequence of DEH element, including ISPpu12, have been investigated, and the results from the experiments studying its transposition and associated effects are presented.

The replication terminus region of the Escherichia coli chromosome can be deleted without any apparent ill effects to the organism. However, when a 44- kb segment corresponding to the 31-min region of the replication terminus segment of the Escherichia coli chromosome was cloned, results showed that a substantial number of normal sized proteins are expressed. This segment encodes proteins which is in comparison with the coding capacity of the entire E. coli chromosome. There are, however, many inessential coding units within the replication terminus region not expressed under ordinary laboratory conditions.

The mobile genetic element DEH, which contains a dehalogenase function, was genetically characterized. Insertional mutagenesis and subcloning experiments localized the dehalogenase gene (dehI) within DEH, while transformation experiments showed that the intact element expressed dehI in both Pseudomonas putida and Escherichia coli. The direction of transcription was determined, and was found to be regulated by an activator gene designated as dehR(sub 1). The activator is constitutively expressed and interacts with inducers such as 2-monochloropropionate and monochloroacetate to activate dehI expression.

The nature of the gene (deh) containing the dehalogenase function of Pseudomonas putida PP3 was elucidated. The gene was found to be contained in a mobile genetic element designated DEH, which recombined with a number of target plasmids at a high frequency. A novel feature of this mobile element was its insertion into target plasmids at varying insert sizes. Insertion of DEH into RP4.5 was shown to be promiscuous and clustered. Results also suggested that the recombination of deh depended on properties found on DEH, and that the transposon preferentially inserts into other transposon targets (hot spots).