[Mechanisms controlling chromatin structure]

Genomic DNA is highly packaged in eukaryotic cells and occurs in the form of nucleoprotein complex called chromatin. Although high DNA compaction allows to store large amount of genomic information in the cell nuclei, it also restricts the access to DNA regulatory sequences. Therefore, to overcome this issue, chromatin must be subjected to various alterations which are dependent on few interrelated factors: DNA modification, histones variants and modifications, ncRNA, chromatin remodeling complexes and chromatin architecture in nuclei. They allow to multilayer regulation of fragile balance between transcriptionally active euchromatin and inactive heterochromatin. The newest research describe new chromatin elements, e.g. half nucleosomes, bivalent chromatin marker and pointed to few intermediate states between euchromatin and heterochromatin. Variety and remarkable amount of chromatin modifications require existence of multiprotein complexes reading, editing and integrating genomic information. Some of them are able to remodel nucleosomes in order to control access to particular DNA sequence. Due to the complexity of chromatin structure regulation studies describing these mechanisms are fundamental to understanding the eukaryotes life.