ColE plasmid replication in DNA polymerase I-deficient strains of Escherichia coli.

Replication of the non-conjugative plasmids ColE1, ColE2 and Col3 has been examined in a number of DNA polymerase I-deficient strains, two of which contain the amber mutation polA1 along with either of two temperature-sensitive supF amber suppressors. These latter two strains produce reduced amounts of DNA polymerase I polymerizing activity of similar, if not identical properties to that produced by polA+ strains. Our results indicate that the ColE plasmids require different amounts of DNA polymerase I for stable plasmid maintenance. Moreover whereas all three plasmids are maintained in a strain defective in the 5' leads to 3' exonuclease activity of DNA polymerase I, ColE2 and ColE3 are not stably maintained between 30 degrees and 43 degrees in a number of DNA POLYMERASE I-deficient strains that are temperature-sensitive for ColE1 replication.