Map of the control vector, pW-GR, and of experimental vectors indicating the position of extrahelical DNA within the RFP transcription unit. (A) Vector pW-GR map. The vector contains red fluorescent protein (RFP), DsRed-express under the control of inducible promoter TRE-tight. It also contains an insulator element to separate the RFP transcription unit from the inducer elements transcription unit. The inducer elements, rtTA (the tet-activator protein) and tTS (a tet-responsive repressor), and a green fluorescent protein (GFP), ZsGreen1, are under the control of the constitutive elongation factor 1-α (EF1-α) promoter. The vector also contains the F1-origin of replication (F1ori) for single strand phage packaging, and bacterial propagation components, ColE1 (E. coli origin of replication) and Ampr (ampicillin resistance gene). (B) Vector pW-GR-stem–loop, transcribed strand, has an extrahelical stem–loop on the transcribed strand of the RFP transcription unit. The non-transcribed strand (red) codes for RFP, while the transcribed strand with the stem loop codes for a truncated, non-fluorescent protein. ( C) pW-GR-stem–loop, non-transcribed strand. (D) pW-GR-loop, transcribed strand. (E) pW-GR-loop, non-transcribed strand.