FIG. 1.

Map of the pAD1 regulatory region with features relating to control of the pheromone response. Regulation is geared to controlling transcriptional readthrough of the two transcription terminator sites t1 and t2 from the iad promoter. The pheromone (cAD1) is imported into the cell via a host-encoded uptake system, a process aided by the plasmid-encoded surface protein TraC. The negatively regulating (neg. reg.) TraA binds directly to cAD1, which results in an upregulation of transcription from the iad promoter, some of which passes through the terminators to ultimately generate TraE1. The transcript mD is present at high levels in the uninduced state and plays a significant role in preventing transcriptional readthrough of t1; it becomes greatly reduced upon induction. The traB product is involved in shutdown of endogenous cAD1 in plasmid-containing cells. traC encodes a surface protein that binds to exogenous pheromone (43). Arrows below the map indicate relative degrees of transcription in various regions; horizontal arrows above the map represent orientations of the indicated determinants.