Figure 43-2: Simple examples of plasmid expression vectors using lambda promoters. Upper: In each diagram the relevant elements of lambda within the plasmid vector are located within the solid segment. Transcription in pKC30 is driven from p(L) and is blocked by lambda repressor provided in trans (80). The resulting transcript includes nut(L), the site at which N protein can interact with RNA polymerase to enable transcription to proceed beyond stop signals. A coding sequence inserted at the HpaI site will be expressed if it includes a rbs. N protein can be provided in trans following derepression of the defective cro-prophage that encodes repressor. In the presence of N protein transcription will read through the termination signal t(1). Middle: Transcription in pCVQ2 is driven from pR, and repressor is provided by the cI gene (cI857) present on the plasmid (76). The cI gene is transcribed from p(RM), a promoter that is autogenously regulated by lambda repressor. The lambda sequence includes the Shine-Dalgarno sequence and initiation codon of the cro gene. Lower: Transcription in pQTE is driven from the late promoter (22). Q gene product is essential for transcription from p(R)? to proceed through t(R)?. Derepression of the lac promoter activates transcription of Q. Coding sequences inserted downstream of p(R)? will be translated if they have a rbs.