The lonmutants of Escherichia coli grow apparently normally except that, after temporary periods of inhibition of deoxyribonucleic acid synthesis, septum formation is specifically inhibited. Under these conditions, long, multinucleate, nonseptate filaments result. The lon-mutation also creates a defect such that wild-type bacteriophage X fails to lysogenize lonmutants efficiently and consequently forms clear plaques on a lonhost. Two lines of evidence suggest that this failure probably results from interference with expression of the AcI gene, which codes for repressor, or with repressor action:* (i) when a Ionmutant was infected with a XcII, cIII, or cY mutant, there was an additive effect between the lonmutation and the Xc mutations upon reduction of lysogenization frequency; and (ii) lonmutants permitted the growth of the Xcro mutant under conditions in which the repressor was active. The isolation of A mutants (Xtp) which gained the ability to form turbid plaques on loncells is also reported. 1326 on August 5, 2020 by guest
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