This family consists of the yeast trans-acting factor B and C (REP1 and 2) proteins. The yeast plasmid stability system consists of two plasmid-coded proteins, Rep1 and Rep2, and a cis-acting locus, STB. The Rep proteins show both self- and cross-interactions in vivo and in vitro, and bind to the STB DNA with assistance from host factor(s). Within the yeast nucleus, the Rep1 and Rep2 proteins tightly associate with STB-containing plasmids into well organised plasmid foci that form a cohesive unit in partitioning. It is generally accepted that the protein-protein and DNA-protein interactions engendered by the Rep-STB system are central to plasmid partitioning. Point mutations in Rep1 that knock out interaction with Rep2 or with STB simultaneously block the ability of these Rep1 variants to support plasmid stability [1].

1: The 2 micron plasmid purloins the yeast cohesin complex: a mechanism for coupling plasmid partitioning and chromosome segregation? Mehta S, Yang XM, Chan CS, Dobson MJ, Jayaram M, Velmurugan S; J Cell Biol 2002;158:625-637. PMID:12177044