Analysis of the open region and of DNA-protein contacts of archaeal RNA polymerase transcription complexes during transition from initiation to elongation.

The archaeal transcriptional machinery is polymerase II (pol II)-like but does not require ATP or TFIIH for open complex formation. We have used enzymatic and chemical probes to follow the movement of Pyrococcus RNA polymerase (RNAP) along the glutamate dehydrogenase gene during transcription initiation and transition to elongation. RNAP was stalled between registers +5 and +20 using C-minus cassettes. The upstream edge of RNAP was in close contact with the archaeal transcription factors TATA box-binding protein/transcription factor B in complexes stalled at position +5. Movement of the downstream edge of the RNAP was not detected by exonuclease III footprinting until register +8. A first structural transition characterized by movement of the upstream edge of RNAP was observed at registers +6/+7. A major transition was observed at registers +10/+11. In complexes stalled at these positions also the downstream edge of RNA polymerase started translocation, and reclosure of the initially open complex occurred indicating promoter clearance. Between registers +11 and +20 both RNAP and transcription bubble moved synchronously with RNA synthesis. The distance of the catalytic center to the front edge of the exo III footprint was approximately 12 nucleotides in all registers. The size of the RNA-DNA hybrid in an early archaeal elongation complex was estimated between 9 and 12 nucleotides. For complexes stalled between positions +10 and +20 the size of the transcription bubble was around 17 nucleotides. This study shows characteristic mechanistic properties of the archaeal system and also similarities to prokaryotic RNAP and pol II.