Stochastic stimulation of 2 mu multicopy plasmid amplification in yeast.

The 2 mu plasmid of Saccharomyces cerevisiae has been used extensively as a vector for foreign protein expression because of its natural amplification to 60-100 copies per cell. The amplification of the 2 mu plasmid occurs through a recombinational mechanism which we have simulated using two free parameters: the FLP recombinase DNA-binding probability and FLP specific enzymatic activity. Model results indicate that a single plasmid amplifies to 5.5-7 copies on average at maximal FLP concentrations and that amplification is approximately proportional to the probability of FLP attachment but independent of its specific enzymatic activity. Thus, FLP overexpression should lead to maximal plasmid amplification. The model predicts the existence of topologically novel replication intermediates.