A conditional lethal mutant of Escherichia coli K12 defective in the 5' leads to 3' exonuclease associated with DNA polymerase I.


A mutant strain of E. coli, initially identified by an abnormally high frequency of recombination, has been found to be defective in the 5' --> 3' exonuclease associated with DNA polymerase I, but not in the polymerase activity. This defect is tolerated at 30 degrees , but is lethal at 43 degrees . Like other polymerase I mutants, the strain is unusually sensitive to methyl methanesulfonate and to ultraviolet irradiation; it is also unable to support the growth of phage lambda defective in general recombination, and shows a reduced rate of joining of 10S "Okazaki fragments." These results demonstrate that a functional DNA polymerase I is essential for normal growth and viability in E. coli K12.




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