DNA sequence-dependent differences in TATA-binding protein-induced DNA bending in solution are highly sensitive to osmolytes

The complex formed between the TATA-binding protein (TBP) and the "TATA box " of eukaryotic class II promoters is the foundation for assembly of the co mplex to which RNA polymerase II is ultimately recruited. TBP binds product ively to canonical and diverse variant TATA sequences with > 100-fold diffe rences in transcription efficiency. Go-crystals of canonical sequences and ttl variant sequences bound to various TBP molecules all have similar to 80 degrees bends. In contrast, the bend angles for TBP.TATA complexes in solu tion, derived from distance distributions, are similar to 80 degrees for a canonical sequence but range from 30 degrees to 62 degrees for five variant sequences (1). We show in this study that the osmolytes used to crystalliz e TBP.TATA complexes induce profound increases in the DNA bends of two tran scriptionally active TBP-bound variant sequences to a common angle of simil ar to 80 degrees but have little effect on a transcriptionally inactive var iant. The effect of osmolyte on the TBP-induced DNA bend of a variant TATA box sequence is also manifest in the kinetics of association, demonstrating a functional consequence of an osmolyte-induced structural change.