pEG plasmid involved in styrene degradation: molecular dimorphism and integration of a segment into the chromosome

In the Pseudomonas fluorescens strain ST the ability to utilize styrene as the sole carbon source is due to the presence of a plasmid, pEG. In the present report we show that pEG contains two inverted repeat sequences and we present evidence indicating that the catabolic genes are localized in these repeats. The region separating the inverted repeats can assume alternative orientations. In the chromosome of strain ST, a 3 kbp region is homologous to sequences present at one end of the plasmid repeats. This region is present in one copy in the chromosome and could be a specific site for integration of the plasmid. We suggest that this sequence, which is present twice in the pEG plasmid and once in the chromosome, might be a transposon-like element.