Transcription factors operate TATA switches via rotational remodeling of local columnar chromatin structure

Our earlier study on the nucleosomes containing TBP binding sites (TATA boxes) indicated that generally the same sequence, which harbors the TATA box, encodes simultaneously an alternative rotational setting of the box, so that the TATA element is either exposed (position "minor groove out") or hidden in position "minor groove in". The sequence elements (dinucleotides) residing on the inner surface of DNA in contact with histone octamers are identified by calculating YR tracks in the promoter regions of the genes - periodically reappearing YR elements, at distances of 10-11 bases from one another. Non-YR elements of the YR tracks are also verified by nucleosome mapping procedure based on alternation of runs of purines with runs of pyrimidines. The tracks observed in yeast promoter regions are found to split into two, passing further downstream either through the TATA element or 4-6 bases toward the tail of the box. The points of splitting which play the role of TATA switches are located in close vicinity or within the transcription factor binding sites. This suggests the regulatory function of transcription factors changing the YR tracks by over- or under-twisting DNA induced by their binding.

Nucleosome repeat lengths and columnar chromatin structure

Thorough quantitative study of nucleosome repeat length (NRL) distributions, conducted in 1992 by J. Widom, resulted in a striking observation that the linker lengths between the nucleosomes are quantized. Comparison of the NRL average values with the MNase cut distances predicted from the hypothetical columnar structure of chromatin (this work) shows a close correspondence between the two. This strongly suggests that the NRL distribution, actually, reflects the dominant role of columnar chromatin structure common for all eukaryotes.