Histones are the proteins promoting the DNA packaging into chromatin fibres. Histone proteins are positively charged possessing several arginine and lysine amino acids binding to the negatively charged DNA. There are two types of Histones:

Core Histones

Linker Histones

H2A, H2B, H3 and H4 are the core histones. Two H3, H4 dimers and two H2A, H2B dimers form an octamer.

Linker histones lock the DNA in place onto the nucleosome and can be removed for transcription.

Histones can be modified to change the amount of packaging a DNA does. The addition of methyl group increases the hydrophobicity of histones. This results in tight DNA packaging.

Acetylation and phosphorylation make the DNA more negatively charged and loosens the DNA packaging.

Enzymes that add methyl groups to histones are called histone methyltransferases. The enzymes that add acetyl groups to the histones are called histone acetyltransferases while the ones that remove the histones are called histone deacetylases.