Reconstruction of the yeast 2 micron plasmid partitioning mechanism.

The effect of the yeast 2 micron circle encoded REP1 and REP2 gene products on plasmid partitioning and copy number control was analyzed by removing the open reading frames from their normal sequence context and transcriptional control regions and directing their expression using heterologous promoters in [cir0] host strains. Both the REP1 and REP2 gene products are directly required at appropriate levels of expression to reconstitute the 2 microns circle partitioning system in conjunction with REP3 and the origin of replication. The level of expression of REP2 appears to be critical to re-establishing proper partitioning and may also play a role in monitoring and thereby regulating the plasmid copy number. Constitutive expression of the REP1 and REP2 open reading frames using heterologous expression signals can be used to reconstruct efficient plasmid partitioning even in the absence of FLP-mediated plasmid amplification and a functional D open reading frame.