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Mutants in a Nonessential Gene of Bacteriophage T4 Which Are Defective in the Degradation of Escherichia coli Deoxyribonucleic Acid ¹

^a Department of Radiation Biology and Biophysics, and Department of Biology, University of Rochester, Rochester, New York 14620

ABSTRACT

Wild-type bacteriophage T4 was enriched for mutants which fail to degrade Escherichia coli deoxyribonucleic acid (DNA) by the following method. E. coli B was labeled in DNA at high specific activity with tritiated thymidine (³H-dT) and infected at low multiplicity with unmutagenized T4D. At 25 min after infection, the culture was lysed and stored. Wild-type T4 degrades the host DNA and incorporates the ³H-dT into the DNA of progeny phage; mutants which fail to degrade the host DNA make unlabeled progeny phage. Wild-type progeny are eventually inactivated by tritium decay; mutants survive. Such mutants were found at a frequency of about 1% in the survivors. Eight mutants are in a single complementation group called denA located near gene 63. Four of these mutants which were examined in detail leave the bulk of the host DNA in large fragments. All eight mutants exhibit much less than normal T4 endonuclease II activity. The mutants produce somewhat fewer phage and less DNA than does wild-type T4.

² Present address: Department of Biophysics, University of Colorado Medical Center, Denver, Colo. 80220.

¹ This work was performed under contract with the U.S. Atomic Energy Commission at the University of Rochester Atomic Energy Project and has been assigned Report No. UR 49-1346. A preliminary report of this work has appeared (Fed. Proc. 29:465, 1970).

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