Characterization of a mini plasmid isolated from Shigella sonnei

A multicopy plasmid, 2.1 kb in size, was isolated from Shigella sonnei and named pKYM. This plasmid is cryptic and isolated along with pKY-1, a ColE1-like plasmid. In this paper, we report the physical map of pKYM and some characters required for its multiplication. The replication of the plasmid DNA does not require DNA polymerase I but depends on protein(s) produced by itself. The plasmid is poorly mobilized by the F factor.