The vegetative course of phage λ development proceeds according to a specific time schedule. Genes flanking the repressor gene c I 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 c III, able to stimulate c I 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 red α ( 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...
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Naomi C. Franklin (1971) studied this question.