The N Operon of Lambda: Extent and Regulation as Observed in Fusions to the Tryptophan Operon of Escherichia coli

Abstract

The vegetative course of phage λ development proceeds according to a specific time schedule. Genes flanking the repressor gene cI are transcribed first: N on the left and the x region on the right. The N gene product is a primary stimulus to further transcription in both directions. Shortly after growth begins, function of genes on the left is curtailed by a product of an early-functioning right gene (Dove, 1968; Radding, 1969; Calendar, 1970).

The present experiments focus on the details of early regulation, particularly regulation of the essential gene N and the region beyond N, where functions nonessential to vegetative development are coded. Among the genes directly to the left of N (Fig. 1), those to be considered are cIII, able to stimulate cI function (Kaiser, 1957), γ, permitting plaque formation on a recA⁻ host (Zissler et al., this volume), and red, promoting phage recombination (Franklin, 1967; Signer et al., 1968). Of these only redα (exo) produces a product, exonuclease (Shulman et al., 1970) that can be assayed with convenience (Little et al., 1967; Radding and Shreffler, 1966).

The approach here has been to replace the genes on the left of N with the genes of the tryptophan (trp) operon of Escherichia coli (Yanofsky, 1967) by genetic fusion (Jacob et al., 1965). The enzymes anthranilate synthetase and phosphoribosyl (PR) transferase, coded in the operator-proximal E and D genes of the trp operon (Fig. 1), are assayed with facility (Ito et al., 1969). Synthesis of these enzymes as part of...