The Sequence and Orientation of Transcription in Bacteriophage

Upon inactivation of the λ repressor protein in a lysogenic cell, transcription commences both leftward (from the l strand) and rightward (from the r strand), beginning at two promoters located to either side of the cI gene (Fig. 1) (Taylor et al., 1967; Ptashne and Hopkins, 1968; Kourilsky et al. 1968; Cohen and Hurwitz, 1968; Oda et al., 1969). The product of the N gene, located just to the left of cI, acts in some way to allow transcription of the genes leftward from N (Kourilsky et al., 1968; Radding and Echols, 1968; Oda et al., 1969; Schwartz, 1970) and is also needed for maximal expression of the x-O-P operon (Heinemann and Spiegelman, this volume) and the Q gene (Butler and Echols, 1970; Hopkins, 1970). The Q gene product (possibly a new σ factor; Naono and Tokuyama, this volume), in turn, is believed to promote the expression of the late...