Attempts to transduce the ultraviolet-sensitive mutator lesion mutU4 into strains deficient in deoxyribonucleic acid polymerase I (polA) were unsuccessful. Mutator recombinants were found when the polA recipient had first been reverted to Pol+ by selection for resistance to methyl methanesulfonate. The inviability of the mutU4 polA double mutant was demonstrated by a reduction in the absolute number of transductants when the recipient was polA as compared with Pol+, and selection was made for

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... rkers very close to mutU4. Double mutants containing mutU4 and polA4, which determines a cold-sensitive polymerase, were unable to grow at 24 C, the nonpermissive temperature. 162 SIEGEL on May 4, 2020 by guest