Fig. 1.

B2 RNA and Alu RNA repress transcription from a template containing a preformed transcription bubble. (A) A model depicting the early stages of the Pol II transcription reaction. RPC, closed complex; RPO, open complex; RPI2,3nt, initiation complex containing 2 or 3 nt RNA. (B) Transcriptional repression by B2 RNA and Alu RNA. (Left) Transcription from the AdMLP on a negatively supercoiled plasmid. (Right) Transcription from the AdMLP on a linear template containing a mismatched region from −9 to +3. Where indicated, ncRNAs (5 nM) were preincubated with Pol II, TFIIB, and TFIIF before the addition of promoter DNA with bound TBP. The number below each lane indicates the amount of transcript normalized to that produced in the absence of ncRNA.