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Such remodeling is principally carried out by 1) covalent histone modifications by specific enzymes, e.g., histone acetyltransferases (HATs), deacetylases, methyltransferases, and kinases, and 2) ATP-dependent chromatin remodeling complexes which either move, eject or restructure nucleosomes. [1]
In molecular biology, SWI/SNF (SWItch/Sucrose Non-Fermentable), [1] [2] is a subfamily of ATP-dependent chromatin remodeling complexes, which is found in eukaryotes.In other words, it is a group of proteins that associate to remodel the way DNA is packaged.
Remodeling proteins work in three distinct ways: they can slide the DNA along the surface of the octamer, replace the one histone dimer with a variant, or remove the histone octamer entirely. No matter the method, in order to modify the nucleosomes, the remodeling complexes require energy from ATP hydrolysis to drive their actions.
Chromatin remodeling enzymes: These enzymes are responsible for promoting euchromatin or heterochromatin formation by a number of processes, particularly modifying histone tails or physically moving the nucleosomes. This in turn, helps regulate gene expression, replication, and how the chromatin interacts with architectural factors. [16]
Note: the histones are omitted in this diagram - only the DNA is shown. With addition of H1, during mitosis the beads-on-a-string structure can coil into a 30 nm-diameter helical structure known as the 30 nm fibre or filament. The precise structure of the chromatin fiber in the cell is not known in detail. [10]
There are four subfamilies of chromatin remodelers: SWI/SNF, INO80, ISW1, and CHD. [2] The RSC complex is a 15-subunit chromatin remodeling complex initially found in Saccharomyces cerevisiae, and is homologous to the SWI/SNF complex found in humans. [1] The RSC complex has ATPase activity in the presence of DNA. [1]
Nucleosome Remodeling Factor (NURF) is an ATP-dependent chromatin remodeling complex first discovered in Drosophila melanogaster (fruit fly) that catalyzes nucleosome sliding in order to regulate gene transcription. It contains an ISWI ATPase, making it part of the ISWI family of chromatin remodeling complexes. NURF is highly conserved among ...
A number of distinct reactions are associated with the term ATP-dependent chromatin remodeling. Remodeling enzymes have been shown to slide nucleosomes along DNA, [50] disrupt histone-DNA contacts to the extent of destabilizing the H2A/H2B dimer [51] [52] and to generate negative superhelical torsion in DNA and chromatin. [53]