Genetic characterization of a bacterial locus involved in the activity of the N function of phage lambda.

We report the genetic mapping of it locus of the Escherichia coli chromosome involved in the expression of the N gene function of phage A. This phage specified function regulates the subsequent transcription of most of the X genome. The bacterial locus involved in N expression, called nus for N utilization substance, maps between aspB at minute 62 and argG at minute 61 of the E. coli chromosome. Two different bacterial variants in which X N function is not active have been used in mapping the nus locus, a mutant of E. coli K12, Nus, and a hybrid bacterium formed by genetic transfer between E. coli and S. typhosa. Although these two bacterial variants exhibit slightly different phenotypes, chromosome transfer studies demonstrate that the same genetic region is involved in the observed N-ineffective phenot,ype. Dominance studies show that in the case of the Nus mutant, the nusf allele is dominant. This suggests that the nus+ allele is responsible for the expression of a function necessary for N product activity. In the case of transfer of the nus region from a Nus mutant to an E. coli-8. typhosa hybrid, the resulting hybrid assumes the phenotype of the Nus mutant. Genetic studies using Pl transduction demonstrate that the same genetic region is involved in the N-ineffective phenotype of the two bacterial variants.