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For example, histone acetylation results in loosening and increased accessibility of chromatin for replication and transcription. Lysine trimethylation can either lead to increased transcriptional activity ( trimethylation of histone H3 lysine 4 ) or transcriptional repression and chromatin compaction ( trimethylation of histone H3, lysine 9 or ...
Additionally, the phosphorylation of histones has been found to play a role in DNA repair and chromatin condensation during cell division. [20] One such example is the phosphorylation of S139 on H2AX histones, which is needed to repair double-stranded breaks in the DNA. [20]
Chromatin remodeling is the dynamic modification of chromatin architecture to allow access of condensed genomic DNA to the ... (for example) methylate or acetylate ...
Heterochromatin vs. euchromatin. Chromatin is found in two varieties: euchromatin and heterochromatin. [7] Originally, the two forms were distinguished cytologically by how intensely they get stained – the euchromatin is less intense, while heterochromatin stains intensely, indicating tighter packing.
Chromatin contains the vast majority of the DNA in an organism, but a small amount inherited maternally can be found in the mitochondria. It is present in most cells, with a few exceptions, for example, red blood cells. Histones are responsible for the first and most basic unit of chromosome organization, the nucleosome.
Structural proteins that bind DNA are well-understood examples of non-specific DNA-protein interactions. Within chromosomes, DNA is held in complexes with structural proteins. These proteins organize the DNA into a compact structure called chromatin.
For example, each human cell has about 1.8 meters of DNA if completely stretched out; however, when wound about histones, this length is reduced to about 9 micrometers (0.09 mm) of 30 nm diameter chromatin fibers. [3] There are five families of histones, which are designated H1/H5 (linker histones), H2, H3, and H4 (core histones).
The hypothesis is that chromatin-DNA interactions are guided by combinations of histone modifications.While it is accepted that modifications (such as methylation, acetylation, ADP-ribosylation, ubiquitination, citrullination, SUMO-ylation [2] and phosphorylation) to histone tails alter chromatin structure, a complete understanding of the precise mechanisms by which these alterations to ...