Conformational dynamics of the tetrameric hemoglobin molecule as revealed by hydrogen exchange: I. Effects of pH, temperature, and ligand binding

Abstract

Transcriptional regulation depends on the appropriate set of positive and negative signals that provide correct gene expression. Studies in eukaryotic gene expression have shown NC2 to be a general repressor of transcription which blocks the interaction between TFIIB and TBP. However, during the last few years NC2 has been found to bind the transcriptionally active promoters and interact with several positive transcription factors. These data suggested a controversial role of NC2 in transcription. Using in vitro transcription on minimal LTR promoter of HIV-1, we show that removal of NC2 from HeLa nuclear extract increases the yield of transcripts as well as unspecific transcription initiation in a template amount dependent manner. Fractions of HeLa nuclear extract containing NC2 can restore basal transcription repression and precise selection of transcription initiation point. This points to a new role for NC2 as a repressor of inaccurate transcription initiation that allows specific transcription to take place.