Figure 1.

Competitor DNA divides transcription into two steps and limits it to a single round. (A) Competitor DNA divides transcription into preinitiation complex formation and RNA synthesis by sequestering free TBP and RNA polymerase II. When competitor DNA is added at point 1 it prevents preinitiation complexes from forming on the promoter. When competitor DNA is added at point 2, after preinitiation complex formation is complete, the competitor prevents further preinitiation complexes from forming during RNA synthesis. (B) ctDNA was titrated into in vitro transcription reactions. When added to reactions before addition of the proteins (point 1 in schematic), ctDNA completely inhibited transcription (dashed line). When added to reactions with nucleotides (point 2 in schematic), ctDNA decreased the level of transcription approximately 8-fold (solid line).