Regions on the F plasmid which affect plasmid maintenance and the ability to segregate into Escherichia coli minicells

Certain derivative mini-F plasmids were found to segregate into Escherichia coli minicells, in contrast to the intact mini-F plasmid which does not. Segregation was not related to the presence or absence of the normal origin of vegetative replication, but appeared to be affected by regions of F which encode replication, incompatibility, copy number control, and partitioning functions. Segregation of mini-F plasmids into minicells was not random; the plasmid concentration in minicells did not correlate with the plasmid concentration in cells. Genes, or gene products, of F from the region spanning the sequences 44.1–49.3F appeared to affect the ability of mini-F plasmids to segregate into minicells. Segregation of mini-F plasmids into minicells was not directly related to stable plasmid inheritance. These results argue for the sequestration of mini-F plasmids in host cells.