A Bacterial Mutation Affecting N Function

Abstract

During a lytic cycle of development of bacteriophage λ, genes N and Q perform regulatory functions (Dove, 1968). The N gene product exerts positive control. The presence of N allows messenger RNA synthesis from the cII-O-P and cIII-exonuclease operons, which originate within the immunity region, to proceed past certain barriers or termination signals on the DNA (Kourilsky et al., 1968; Kumar et al., 1969; Heinemann and Spiegelman, 1970). Two models have been suggested for the action of the product of gene N. The first, called the “antitermination model,” stems from Roberts’ (1969) discovery of an mRNA termination factor called ρ. The N gene product is thought of as antagonizing ρ, thus enabling the RNA polymerase to proceed past the termination signals. The second, called the “activated promoter model,” represents the N gene product as a specific initiation factor allowing transcription to start at promoter sites postulated to exist beyond the termination signals.

We wish to report the isolation of a mutant of Escherichia coli strain K12 in which λ development is blocked at the stage of N gene function. Investigation of this mutant may shed light on the mechanism of N action.

RESULTS
Isolation of the Bacterial Mutant
To obtain bacterial mutants blocked in phage λ and 434 development we employed a selective technique that allows the detection of such mutants whether or not they are killed by abortive phage development. Cells of E. coli K12 galE⁻su⁻ (strain SKB178) were exposed to nitrosoguanidine, allowed to grow in complete medium, then...