Identification of a low-copy-number mutation within the pUB110 replicon and its effect on plasmid stability in Bacillus subtilis.

A mutation (cop1) within the minimal replicon of plasmid pUB110, reducing its copy number from 48 +/- 2 to 11 +/- 2 in a Bacillus subtilis host, was isolated. This mutation is a G----T transversion within the translation control region of the replication initiation gene (repU). The cop1 mutation, when present in the recombinant plasmid, increases both its structural and segregational stability.