In vitro determination of the 30 nm chromatin fiber structure (564.1)

Abstract

To be able to fit 6 ft. of human DNA into a cell’s nucleus, an elaborate organizational system is necessary to compact the genomic DNA first into nucleosomes, and then into a 30 nm chromatin fiber. The ability to figure out the spatial conformation between these nucleosomes is vital in understanding gene regulation of underlying DNA. Literature data support two different models of the chromatin fiber that differ in their geometry and possible impact on the accessibility of the underlying DNA sequence. The “zig‐zag” model uses a straight linker DNA region, while the “solenoid” model illustrates a bent DNA linker, greatly influencing which nucleosomes are in close space in relation to one another. However, there is debate about which of these models actually represents the true structure. High resolution in vivo nucleosome maps show that the length of DNA between two nucleosomes is not constant across a genome. Computational studies have shown that changing this linker‐length can drastically change the available compacted structures accessible to an array of nucleosomes. To determine how much the properties of the linker DNA affect chromatin structure, we are developing a quantitative crosslinking assay. In our studies, we use this method to investigate the linker‐length dependence of chromatin structure in synthetic nucleosome arrays. Initial results have shown evidence for both zig‐zag and solenoid models depending on solution conditions.