Fig. 4.

The toxT 5′ UTR fourU RNA thermometer facilitates temperature-dependent expression of CT. V. cholerae O1 ΔtoxT strains KKV2288 (Classical) and KKV2426 (El Tor) carrying plasmids pKEK1682 (5′-toxT UTR-toxT), pKEK1683 (5′-U5C toxT UTR-toxT), pKEK1685 (5′-U7C toxT UTR- toxT), or pKEK1686 (5′-U5C U7C toxT UTR- toxT) were grown at 25 °C and 37 °C in the presence of 0.1% arabinose and harvested at identical cell densities (OD₆₀₀ = 0.6). mRNA abundance for (A) toxT and (B) ctxB were determined by quantitative RT-PCR (Materials and Methods). (C) Supernatants were assayed for CT.