Mechanism of autoregulation by an archaeal transcriptional repressor.

The basal transcription machinery of archaea corresponds to the core components of the eucaryal RNA polymerase II apparatus. Thus, archaea possess a complex multi-subunit RNA polymerase, a TATA box-binding protein and a protein termed transcription factor B (TFB), which is a homologue of eucaryal transcription factor IIB (TFIIB). Intriguingly, archaeal genome sequencing projects have revealed the existence of homologues of bacterial transcriptional regulators. To investigate the mechanism of transcriptional regulation in archaea we have studied one such molecule, Lrs14, a Sulfolobus solfataricus P2 homologue of the bacterial leucine-responsive regulatory protein, Lrp. We find that purified Lrs14 specifically represses the transcription of its own gene in a reconstituted in vitro transcription system. Furthermore, we show that Lrs14 binding sites overlap the basal promoter elements of the Lrs14 promoter and reveal that binding of Lrs14 to these sites prevents promoter recognition by TATA box-binding protein and TFB.