Abstract
We have identified and analyzed two DNA regions responsible for stable maintenance of a plasmid in the genus Sphingomonas and Escherichia coli. A 37 bp fragment, upstream of the repA gene, is required for stable maintenance of the low-copy-number small plasmid pYAN-2 (4,687 bp) from Sphingobium yanoikuyae. It does not encode any significant protein sequence and has one direct repeat for possible secondary structures. Moreover, a 70 bp fragment, upstream of the above sequence, completely stabilized the unstable pSC101 plasmid in E. coli.