Regulation of copy number and stability of phage lambda derived pTC lambda1 plasmid in the light of the dimer/multimer catastrophe hypothesis

The dimer catastrophe hypothesis has been proposed previously to explain in stability of multicopy plasmids whose partitioning is random, contrary to l ow copy number plasmids which are stably maintained and actively partitione d. Until now, this hypothesis has been investigated using multicopy ColE1 p lasmids. However, for more detailed testing of the dimer/multimer catastrop he hypothesis, one should use a plasmid which can be maintained at either l ow or high copy number and still possesses the same mechanism of replicatio n regulation. Here we used a modified lambda plasmid, pTC lambda 1. The adv antage of this plasmid is that it can be maintained at different copy numbe rs depending on the concentration of an inducer which stimulates the initia tion of plasmid replication. Results obtained with this plasmid in recombin ation proficient and deficient cells generally support the dimer/multimer c atastrophe hypothesis, but also suggest some modification in the model. (C) 1999 Published by Elsevier Science B.V. All rights reserved.