REPLICATION AND SEGREGATION OF A MINIF PLASMID DURING THE DIVISION CYCLE OF ESCHERICHIA-COLI

Replication of the miniF plasmid pML31 was examined during the divisio n cycle of Escherichia coli growing with doubling times between 10 and 90 min at 37 degrees C and compared to the replication of plasmid pBR 322 and the minichromosome pAL70. The replication pattern of pML31 was indistinguishable from that of pBR322 at all growth rates and very di fferent from the cell-cycle-specific replication of the minichromosome . It is concluded that both pML31 and pBR322 plasmids can replicate at an stages of the division cycle, with a probability of replication th at increases gradually, but perhaps not exponentially, during the cycl e. In contrast, the modes of segregation of pML31 and pBR322 plasmids into daughter cells at division appeared to differ, raising the possib ility that pML31 may segregate in a nonrandom fashion similar to that of chromosomes and minichromosomes.