Nucleosome structural features and intrinsic properties of the TATAAACGCC repeat sequence

Nucleosomes, the fundamental building blocks of chromatin, play an architectural role in ensuring the integrity of the genome and act as a regulator of transcription. Intrinsic properties of the underlying DNA sequence, such as flexibility and intrinsic bending, direct the formation of nucleosomes. We have earlier identified genomic nucleosome-positioning sequences with increased in vitro ability for nucleosome formation. One group of sequences bearing a 10-base pair consensus repeat sequence of TATAAACGCC had the highest reported nucleosome affinity from genomic material. Here, we report the intrinsic physical properties of this sequence and the structural details of the nucleosome it forms, as analyzed by footprinting techniques. The minor groove is buried toward the histone octamer at the AA steps and facing outwards at the CC steps. By cyclization kinetics, the overall helical repeat of the free DNA sequence was found to be 10.5 base pairs/turn. Our experiments also showed that this sequence is highly flexible, having a J-factor 25-fold higher than that of random sequence DNA. In addition, the data suggest that twist flexibility is an important determinant for translational nucleosome positioning, particularly over the dyad region.