Protein binding interactions at the STB locus of the yeast 2 microns plasmid

The cis-acting STB locus has been shown to be a multiple protein binding site. STB-specific binding activity was detected in a normally insoluble yeast cell protein fraction, suggesting association with a subcellular structure. Both 2 microns-encoded and host-encoded STB-binding activities were identified. The 2 microns proteins showed contrasting STB-binding activities: C (REP2) protein acted cooperatively with the host factor to promote STB binding; B (REP1) protein also acted in association with the host factor, but showed a dual action, opposing or facilitating binding, depending upon concentration; D (RAF) exhibited rapid binding and antagonism to host factor binding. FLP did not bind, but promoted host factor dissociation. The implications of these activities for the molecular mechanism of 2 microns plasmid inheritance are considered.