CH/pi interactions in the crystal structure of TATA-box binding protein/DNA complexes.

Crystal structures of TATA box-binding proteins (TBP) of various sources bound to their promoter DNA (TATA box) were analyzed with use of our program CHPI. A number of short CH/Csp2 contacts have been unveiled in these complexes at the boundary of TBP and the TATA box minor groove. The result was discussed in the context of the CH/pi interaction. Thus, the nature of nonpolar forces, reported in the past at the interface of the two components, has been attributed to the CH/pi interaction. Furthermore, many CH/pi contacts have been disclosed within the same strand of the promoter DNA. The structure of the TATA element, partially unwound and severely bent on complexation, seems to be stabilized by CH/pi interactions; H2' of the deoxyribose moiety and the methyl group in the thymine nucleotide play the primary role.