Specific in vitro binding of a plasmid to a membrane fraction of Bacillus subtilis

A model system has been developed to study the in vitro binding of a plasmid to the membrane fraction from Bacillus subtilis. The plasmid DNA molecule used in these studies was pSL103 (8.0 kilobases), a chimeric plasmid consisting of a Staphylococcus aureus plasmid (pUB110, 4.5 kilobases) and a DNA fragment (3.5 kilobases) from Bacillus pumilus carrying trpC+ gene. This plasmid replicates in B. subtilis cells, and its in vivo membrane binding (as well as its replication) is dependent on the product of a DNA initiation gene, dna-1, of B. subtilis. In this paper we demonstrate the in vitro specific binding of exogenous pSL103 to the isolated membrane fraction. This in vitro binding is specific to the origin-containing portion (pUB110) of pSL103. The trpC+-carrying portion neither binds to the membrane fraction nor competes with pSL103 for binding to the membrane fraction in vitro. ColE1 plasmid, which does not replicate in B. subtilis, neither binds to the B. subtilis membrane fraction nor competes with pSL103 for binding.