Nucleosomes form tight, sheltered structures that protect DNA while remaining flexible enough to allow polymerase to access the DNA. Nucleosomes also modify genetic activity, playing a role in determining the expression of genetic traits.
Nuclesomes perform a paradoxical task, protecting DNA from damage and contamination while allowing polymerase to transcribe messenger RNA and replicate the DNA when the cell divides. Scientists do not completely understand how nucleosomes manage to remain stable and labile at the same time, according to the Research Collaboratory for Structural Bioinformatics. Research suggests that the nucleosome may partially unwind in the reading process, allowing proteins to read genetic information one loop at a time.
Scientists understand the role nucleosomes play in gene expression better than the access-control mechanism. Each nucleosome contains eight histone proteins that tightly bond to DNA. Histone proteins, unlike most other proteins, are not globular in shape, but instead feature a long tail. This tail can comprise almost a quarter of the length of a histone protein. The histone tail reaches outwards towards neighboring nucleosomes and binds them together, forming a tight bond that regulatory enzymes weaken in order to facilitate gene expression. The manner in which nucleosomes bond is responsible for making particular gene sequences more accessible than others.