Replication of plasmids in mutants of Escherichia coli temperature-sensitive for initiation of deoxyribonucleic acid synthesis

Plasmid deoxyribonucleic acid (DNA) replication was studied in Escherichia coli hosts carrying temperature-sensitive (ts) initiation mutations. The replication of the R plasmid NR1 continues at the nonpermissive temperature in a ts dnaA mutant host but at a decreasing rate in proportion to the residual chromosome synthesis. The replication of NR1, as well as of the F plasmid F′lac, ceases immediately at the nonpermissive temperature in a ts dnaC mutant host. The ability to reinitiate R plasmid replication in the absence of protein or ribonucleic acid synthesis is accumulated at the nonpermissive temperature in a dnaC mutant host.