Figure 1.

Map of bacteriophage λ replication region present in standard λ plasmids (also those used in this work). Genes cro, cII, O, P, and ren are marked (these plasmids do not contain a gene coding for the CI repressor). All promoters (p) and terminators (t) are indicated. The p_R promoter region contains the operator sites, and the p_M promoter (whose activity could potentially play a role in transcription initiated at p_R) is repressed by the cro gene product and cannot be activated in the absence of the CI protein. Transcripts are presented as arrows with arrowheads indicating directionality of transcription. Origin of λ DNA replication (oriλ) is located in the middle of the O gene. Restriction sites for HindIII, NsiI, BstXI, and DraI endonucleases (used for preparation of DNA fragments for templates in in vitro transcription reactions) are indicated.