Search

Site-specific recognition of DNA in eukaryotic organisms depends on the arrangement of nucleosomes in chromatin. In the yeast Saccharomyces cerevisiae, ISW1a and related chromatin remodelling factors are implicated in establishing the nucleosome repeat during replication and altering nucleosome position to affect gene activity. Here we have solved the crystal structures of S. cerevisiae ISW1a lacking its ATPase domain both alone and with dNa bound at resolutions of 3.25 Å and 3.60 Å, respectively, and we have visualized two different nucleosome-containing remodelling complexes using cryo-electron microscopy. The composite X-ray and electron microscopy structures combined with site-directed photocrosslinking analyses of these complexes suggest that ISW1a uses a dinucleosome substrate for chromatin remodelling. Results from a remodelling assay corroborate the dinucleosome model. We show how a chromatin remodelling factor could set the spacing between two adjacent nucleosomes acting as a 'protein ruler'., DNA in eukaryotic cells is packaged in nucleosomes to comprise chromatin, serving generally to protect DNA integrity and to repress gene transcription. Chromatin structure depends on regular arrays of nucleosomes [...]

Author(s): Thomas Schalch [1]; Sylwia Duda [1]; David F. Sargent [1]; Timothy J. Richmond (corresponding author) [1] DNA in eukaryotic chromosomes is organized in arrays of nucleosomes compacted into chromatin [...]

Researchers have solved the high resolution X-ray structure of the nucleosome core particle. The crystal structure of the nucleosome core particle of chromatin includes a 146 base pair DNA molecule. The atomic model shows these pairs in a superhelix around the histone protein octamer. Each histone contains a histone fold domain and there are well-ordered structure elements extending from the histone motif. These two aspects determine the histone/histone and histone/DNA interactions. The DNA differs from ideal superhelix geometry due to the lack of uniformity in these interactions.

A study of the crystal structure of a yeast complex shows that the transcription factor IIA (TFIIA) has a boot-like appearance and consists of a 12-strand beta-barrel and a four-helix bundle motif. The beta-barrel helps in extending the TATA-box-binding protein (TBP) beta-sheet. The beta-barrel assists in bridging over the DNA major groove immediately against the TATA box. The four-helix bundle offers its substantial contribution to the surface of the TFIIA/TBP/DNA complex. The complex interacts with additional transcription factors.