title: Multimerization of high copy number plasmids causes instability: CoIE1 encodes a determinant essential for plasmid monomerization and stability.
abstract: Although the natural multicopy plasmid CoIE1 is maintained stably under most growth conditions, plasmid cloning vectors related to it are relatively unstable, being lost at frequencies of 10(-2)-10(-5) per cell per generation. Evidence suggests that CoIE1 and related plasmids are partitioned randomly at cell division and that plasmid stability is correlated inversely with plasmid multimerization; factors or conditions that reduce multimerization increase stability. Cells containing plasmid multimers segregate plasmid-free cells because the multimers are maintained at lower copy numbers than monomers, as predicted by origin-counting models for copy number control. CoIE1 is stable because it encodes a determinant, cer, that is necessary for recA-, recF-, and recE-independent recombination events that efficiently convert any multimers to monomers. We have localized monomerizing and stability determinants of CoIE1 to within a 0.38 kb region that, when cloned into plasmid vectors, greatly increases their stability.
mesh_terms: D000667:Ampicillin / Q000633:toxicity; D003086:Bacteriocin Plasmids; D003001:Cloning, Molecular; D004262:DNA Restriction Enzymes; D004926:Escherichia coli / Q000235:genetics*; D005822:Genetic Vectors; D007700:Kinetics; D010403:Penicillin Resistance; D010957:Plasmids
chemical_list: D000667:Ampicillin; D004262:DNA Restriction Enzymes