Fig. 3.

Only the downstream, and not the upstream, EUO-binding site in the omcAB promoter is important for repression by EUO.

A. Diagram showing transcription templates used to test the roles of the two EUO-binding sites in repression of the omcAB promoter. The template labelled ‘Both sites’ contains the two native EUO-binding sites upstream of omcAB in the region from +5 to –122. ‘Downstream site only’ is a truncation from –55 to +5 containing only the downstream EUO-binding site. ‘Upstream site only’ contains the omcAB promoter region from –122 to +5 in which the downstream EUO-binding site has been disrupted by a 9 bp substitution (M3 in Fig. 2). Positions of the EUO-binding sites, and the –10 and –35 promoter elements are shown.

B. In vitro transcription of these three transcription templates by E. coli RNA polymerase in the absence or presence of 2.5 μM C. trachomatis EUO.