SpxA1 and SpxA2 specifically enhance transcription of oxidative stress genes. In vitro transcription (IVT) reactions were performed by incubating selected DNA templates with S. mutans RNAP and nucleotides including [α-32P]UTP in the absence (0) or presence of purified His-tagged protein: SpxA1 (A1), SpxA2 (A2), and SpxA1 and SpxA2 combined (A1/A2). Reactions were performed at 37°C. Radiolabeled RNA transcripts were precipitated, applied to 8% urea PAGE, and visualized by exposure to a phosphorimager screen. (A) IVT reactions performed with template DNA for ahpC, sodA, or tpx. (B) His-tagged CodY failed to enhance transcription of sodA or tpx, and SpxA1 failed to enhance transcription of mleS. (C) IVT reactions were performed with increasing amounts of SpxA1 or SpxA2 using the sodA or tpx DNA templates. Representatives of three or more independent reactions are shown. Densitometry was performed with ImageJ software.