Cooperative effects of bacterial mutations affecting [lambda] N gene expression : I. Isolation and characterization of a nusB mutant

Abstract

We report the isolation and characterization of an Escherichia coli mutant which limits the growth of phage [lambda] by inhibiting the expression of the N gene regulatory function. The mutation involved maps near minute 11 of the E. coli chromosome and dominance tests show that the mutant allele is recessive to the wild one. Therefore, we conclude that the locus involved normally codes for a function necessary for N expression. Another mutant which exhibits a similar phenotype has previously been reported and the mutation involved, in that case, maps at minute 61. This mutant is called Nus (N utilization substance); we have named the locus at minute 61 nusA, and the locus at minute 11, nusB. Although the nusA allele is not found in Salmonella typhosa, our studies demonstrate that the nusA allele is found in this closely related enterobacteriaciae.A nusA-1 nusB-5 double mutant was constructed and exhibited a far more restrictive effect on [lambda] growth than either of the single nus mutants. Further, we have constructed a [lambda] variant which carries the nusB+ allele. This phage plates on nusB-5 mutants under restrictive conditions, but not on the nusA-1 mutants.