Isolation and structure of the replicon of the promiscuous plasmid pCU1.

Evidence is presented to indicate that a PvuII fragment of approx. 2 kb isolated from the 39-kb IncN-group plasmid pCU-1 contains all plasmid-borne determinants for stable maintenance as an extrachromosomal element in Escherichia coli K-12. The fragment was sequenced. The features of this sequence include a group of 13 direct tandem repeats of 37 bp and a second group of two other direct repeats of 30 bp flanking a third partial member of this group. In addition, for a 19-bp sequence that overlaps a member of this second group, there are inverted repeats that straddle the members of the first group. There are three open reading frames within the fragment. We compare features of this sequence with that of other plasmid replicons and draw attention to similar and to dissimilar features.