Temperature sensitive replication plasmids are passively distributed during cell division at non-permissive temperature: a new model for replicon duplication and partitioning.

To see whether plasmid molecules in bacteria are equally partitioned or randomly distributed at cell division, the segregation properties of temperature sensitive replication mutants of the E. coli plasmid pSC101 were tested at non-permissive temperature. The results support the idea that at least unreplicated molecules are passively distributed and thus the Equipartition Model is unlikely even under physiological conditions if plasmids replicate randomly. Therefore, we developed a new model which involves the Random Replication Hypothesis and assumes that only the two products of the last plasmid replication event are actively partitioned into two daughter cells and the others are randomly distributed. Mathematical studies revealed that the incompatibility segregation rate predicted by this model fits the experimental data.