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. 2018 Mar 7;10(3):115. doi: 10.3390/v10030115

Figure 3.

Figure 3

CII trans-complementation assay. Top shows complementation results (additional examples are shown in Figures S2 and S3). The cartoon shows the sequential steps, A to D required for CII complementation. Each step is indicated by either dotted (steps A and D) or solid (steps B and C) lines. Steps: A cII expression occurs from plasmid pcIpR-cII-timm in 594 cells upon shifting cells grown at 30 °C to 37–42 °C. This inactivates the CIλ repressor, enabling transcription from plasmid promoter pR through gene cII. B CII protein encoded by plasmid stimulates repressor-establishment transcription from promoter pE on phage genome after 594 [pcIpE-cII-timm] cells are infected with phage λimm434cII2002. C High expression of the CI434 repressor protein occurs from CII-stimulated pE-mRNA transcribed from infecting phage genome. D CI434 repressor binds the oL434 and oR434 operator sites preventing leftward and rightward transcription and blocking lytic phage growth. The potential for OOP RNA expression from plasmid pcIpR-cII-oop-pO nullifies CII-activation of pE-dependent CI434 expression at 37–39 °C. The results for infections with λimm434cII68 were identical to infections with λimm434cII2002.