Abstract
We have described a temperature-sensitive, radiation-sensitive mutant of Escherichia coli. In vitro assays have demonstrated that DNA ligase activity is markedly reduced in this strain relative to that of the parent strain. Okazaki fragments of newly replicated DNA accumulate in this mutant strain upon growth at the restrictive temperature. These results imply that the same enzyme, DNA ligase, functions both in normal semiconservative replication and in nonconservative repair replication of DNA.