Efficiency of Escherichia coli repair processes on uv-damaged transforming plasmid DNA

A comparison has been made of the efficiencies with which the dark repair processes of Escherichia coli act on ultraviolet irradiated bacterial chromosomal DNA and ultraviolet damaged transforming plasmid DNA. It is shown that postreplicational repair pathways act very inefficiently on transforming plasmid DNA, and that the majority of repair is carried out by excision repair pathways. However, even excision repair pathways act less efficiently on damaged plasmid DNA than they do on chromosomal DNA. The large effect of mutations in recB on plasmid survival suggests that the product of this gene may be essential for the excision repair pathways which act on plasmid DNA, but not for those which act on chromosomal DNA.