Studies on the E. coli groNB (nusB) gene which affects bacteriophage λ N gene function

Summary

Escherichia coli mutants, called groNB, which block the growth of bacteriophage λ at the level of action of the gene N product, have been isolated as survivors at 42°C of bacteria carrying a) the defective prophage λbio1 1 i ^λ cI857 ∇H1 or b) the pcR1 plasmid containing the EcoRI immunity fragment of phage λcI857. In addition, groNB bacterial mutants have been isolated at 37° C, as large colony formers in the presence of λi ^λ cI h ⁴³⁴, λi ^λ cI h ^λ, and λi ^λ cI h ⁸⁰ phage. The groNB locus is located at 9 minute of the E. coli genetic map with the order of the neighboring loci being proC tsx groNB purE. Most groNB mutations isolated at 42° C were found to interfere in addition with bacterial growth at low temperatures, since (a) the GroNB phenotypes of λ growth inhibition and bacterial cold sensitivity cannot be separated by P1 transduction, and (b) some cold resistant revertants simultaneously become Gro⁺ for λ growth. Lambda transducing phages carrying the groNB ⁺ bacterial gene have been isolated. GroNB mutant bacterial lysogenized by the transducing phage acquire the Gro⁺ phenotype and simultaneously the cold resistant phenotype, suggesting that the groNB mutations are recessive to the wild-type gene.