R factor deoxyribonucleic acid in chromosomeless progeny of Escherichia coli.

The deoxyribonucleic acid (DNA) of resistance (R) factor 222 carried by Escherichia coli strain P678-54 was found in the normally chromosomeless progeny (minicells) of that strain. The entry of the R222 DNA into minicells appears to be via segregation at the time of their formation from normal cells. The R222 DNA can replicate in minicells although the extent of its replication appears to be limited. An analysis of the R222 DNA structure indicates that it exists in minicells as double-stranded linear, open circular, and twisted circular monomers (molecular weight, about 6.2 x 10(7) daltons). The monomers visualized by electron microscopy are 31.0 +/- 0.5 mum in length. An examination of the effect of acridine orange on the replication of R222 and colicin E1 DNA indicates the dye intereferes with plasmid DNA replication.