TFIID

Binding of the general transcription factor TFIID, to the core promoter is the first step in the assembly of the whole transcriptional machinery. Using single particle analysis we obtained a 3-D model of TFIID and TFIID-A-B by negative stain, and located the position of TBP by antibody labeling (Andel et al., Science 1999). We have recently led the implementation of a new statistical method to calculate the 3-D variance and covariance of a cryo-EM reconstruction. This method can identify mobile regions and produce multiple conformationally-distinct models that more accurately mirror the population found in the protein sample. We have first applied this methodology to analysis of the human basal transcription factors TFIID and RNA Pol II. We found that a number of discrete structural elements in TFIID move in a concerted manner via hinges in the structure (Grob et al., Structure 2006). We propose that this type of conformational versatility is likely to be an intrinsic property of large macromolecular complexes and important for their biological function.