Restoration of polarity by N-deficiency in lambda phage containing a translocated trp operon segment

Abstract

When translation of trp mRNA is terminated by a nonsense codon or by antibiotics like chloramphenicol, the amount of the mRNA distal to the blocked ribosomes is found at much lower levels (“polarity”). Polarity is alleviated when the trp mRNA is formed as part of a long transcript from the phage λ promoter P _L(Segawa and Imamoto, 1974; Franklin, 1974); but the relief of polarity is itself largely dependent on the λ protein N. In a phage that joins the trp operon segment (trpD, C, B, A) to a point distal to the N gene, lacking the t _Lsite, synthesis of trp mRNA starting at the P _Lpromoter continues even when translation is generally inhibited by chloramphenicol, but in the absence of functional N gene product synthesis of the mRNA can be blocked by the antibiotic. Unexpectedly, in the absence of N function, even when translation is occurring, weak termination of transcription occurs at some sites in the translocated trp operon.