Mechanism for chromosome and minichromosome segregation in Escherichia coli

A mechanism for the segregation of chromosomes and minichromosomes into daughter cells during division of Escherichia coli is presented. It is based on the idea that the cell envelope contains a large number of sites capable of binding to the chromosomal replication origin, oriC, and that a polymerizing DNA strand becomes attached to one of the sites at initiation of a round of replication. The attachment sites are distributed throughout the actively growing cell envelope, i.e. lateral envelope and septum, but not in the existing cell poles. This asymmetric distribution of oriC attachment sites accounts for the experimentally observed non-random chromosome and minichromosome segregation, and for the variation in the degree of non-random segregation with cell strain and growth rate. The multi-site attachment concept also accounts for the unstable maintenance of minichromosomes.