Question

There are multiple methods of chromatin remodeling. What are two that are covered in your text? Give a brief description of each one. (Be sure to include the three possible outcomes of ATP-dependent chromatin remodeling in your description of that method.)

Answer 1

Chromatin remodeling is principally carried out by:

1. Covalent histone modification
2. ATP dependent chromatin remodeling

1. Covalent modifications are done by histone modifying enzymes, i.e., methyltransferases, histone acetyltransferases, deacetylases and kinases. Meyhylases cause methylation of lysine and arginine residues in H3 and H4 and cause further DNA condensation around histone thereby preventing the binding of transcription factors to the DNA that contribute to gene repression.

HAT (histone acetyl transferase) is used for the acetylation; HDAC (histone deacetylase) is used for the deacetylation. Histone acetylation relaxes the condensation of chromatin and exposes DNA for TF binding which results in increased gene expression.

2. ATP-dependent chromatin-remodeling complexes have ATPase domain and through the hydrolysis of ATP these complexes repositioning of nucleosomes thus regulate gene expression by either moving, rotation or modification of nucleosomes.

ISWI:After DNA replication and the maintenance of higher-order chromatin structures, the ISWI family remodelers play central roles in chromatin assembly.

SWI / SNF: These remodelers nucleosomal dysfunction.

NuRD / Mi-2 / CHD remodeling complexes: They mediate transcriptional repression mainly in the nucleus.