Histones are proteins that provide structural support to a chromosome. Each chromosome contains the DNA molecule wrapped around the histone protein providing a more compact shape to the chromosomes.
In addition, histone proteins play a role in the regulation of gene expression. Histones affect the accessibility of DNA to the binding of RNA polymerase and transcription factors. Compact and closed chromatin has DNA tightly bound so that the transcriptional machinery cannot access the DNA and genes remain inactive (see top part of diagram). By modifying the histone tail, the chromatin is loosened and DNA is not as tightly bound. The genes can become accessible by transcription and are now active (see bottom part of diagram).19
Distinct combinations of chemical modifications of histones dictate varying responses. Below is a list of these factors:
- Acetylation
- Phosphorylation
- Methylation
- Ubiquitination
- Ribosylation
- Glycosylation
