Figure 4. Comparison of the SW1 promoter and regulatory structure with the filamentous phage CTXФ.

For CTXФ, the transcription directions of the replication gene rstA and the repressor gene rstR are reversed and share a compact regulatory region, which harbours 3 RstR binding sites. For SW1, the transcription directions of fpsA and fpsR are arranged in an uncommon opposite direction. The regulatory region contains two long 5′UTRs with overlapping portions, and a long 3′UTR is found downstream of the fpsR coding region. In addition, the phage-encoded regulator FpsR is able to bind to the promoter region of fpsA gene while not to fpsR gene. The primer pairs used in EMSA experiment are indicated by black arrows.