Key Difference – Histone vs Nonhistone Proteins
Chromatin is the condensed form of DNA within chromosomes. It is a complex of DNA and proteins. Proteins provide the structure to chromatin and stabilize the DNA inside the small volume of the nucleus. Proteins involved in stabilizing chromatin structure are two types named histone proteins and nonhistone proteins. The key difference between histone and nonhistone proteins is that histone proteins are the spools in which DNA binds while nonhistone proteins provide the scaffolding structure to DNA. Histone and nonhistone proteins work together to organize and maintain chromosomes.
CONTENTS
1. Overview and Key Difference
2. What are Histone Proteins
3. What are Nonhistone Proteins
4. Side by Side Comparison – Histone vs Nonhistone Proteins
5. Summary
What are Histone Proteins?
Histone proteins are referred to as the major protein component of chromatin. These proteins provide essential structures to wind DNA and reduce its length to form chromatin. Histone proteins act as spools in which DNA winds and stabilizes. Therefore, they are extremely important in organizing chromosomes and packaging genetic material inside the nucleus. If histone proteins do not exist, chromosomes would not exist and unwound DNA will stretch into a long length making them hard to locate within the nucleus.
Histone proteins work with nonhistone proteins to stabilize the structure of DNA. The presence of nonhistone proteins is essential for the function of histone proteins. Histone proteins become core protein molecules to form nucleosomes that are basic units of chromatin. A nucleosome is made up of eight histone proteins and the DNA. The formation of the nucleosome is done by histone proteins acting as spools for DNA to wind. Histone proteins are also involved in gene regulation. They help to control gene expression. Histone proteins are highly conserved in species, unlike nonhistone proteins.
Figure 01: Histone proteins
What are Nonhistone Proteins?
Nonhistone proteins are another type of proteins associated with DNA in chromatin structure. They provide the scaffolding structure to DNA. They function together with histone proteins to organize chromosomes within the nucleus. When histones are removed from the chromatin, the remaining proteins are referred as nonhistone proteins. Scaffold proteins, heterochromatin protein 1, DNA polymerase, polycomb, and other motor proteins are examples of nonhistone proteins. In addition to acting as scaffolding proteins, nonhistone proteins do several other structural and regulatory functions as well in the cells. However, the main function of nonhistone proteins is the compaction of chromatin in chromosomes and organization of chromosomes inside the nucleus.
What is the difference between Histone and Nonhistone Proteins?
Histone vs Nonhistone Proteins |
|
| Histone proteins are the principal protein component of chromatin. | Nonhistone proteins are components of chromatin. |
| Major Function | |
| They act as spools for DNA to wind and become shorter in length. | They act mainly as scaffolding proteins for DNA. |
| Types | |
| H1/H5, H2A, H2B, H3, and H4 are types of histones. | Scaffold proteins, Heterochromatin Protein 1, DNA polymerase, Polycomb, etc. are some types of nonhistones. |
| Involvement of Nucleosome | |
| Histone proteins are the core proteins of a nucleosome. | Nonhistone proteins are not a part of a nucleosome. |
| Conserved Sequence | |
| Histone proteins are conserved across species. | Nonhistone proteins are not conserved across species. |
| Role in Gene Expression | |
| Histone proteins are involved in gene expression regulation | Nonhistone proteins are not involved in gene expression regulation |
Summary – Histone vs Nonhistone Proteins
Histone and nonhistone proteins are two types of proteins found in chromatin of eukaryotic organisms. DNA is wound around histone proteins and form the fundamental unit of chromatin called nucleosome. The major function of histone proteins is to act as spools for DNA to wind and stabilize. Nonhistone proteins act as the scaffolding structure of chromatin. This is the main difference between histone and nonhistone proteins. If histone proteins are removed from chromatin, the remaining protein part can be referred as nonhistone proteins. They are also important in organizing and compaction of chromatin into chromosomes within the nucleus. Both proteins work together. Histones are responsible for the formation of the structure of chromosomes while nonhistone proteins are responsible for maintenance of the chromosomal structure.
References
1. Curtis Seubert. “The Difference Between Histone & Nonhistone.” Sciencing. Leaf Group, 24 Apr. 2017. Web. 15 May 2017.
2. “Histone/Histones.” Nature News. Nature Publishing Group, n.d. Web. 15 May 2017
3. Mariño-Ramírez, Leonardo, Maricel G. Kann, Benjamin A. Shoemaker, and David Landsman. “Histone structure and nucleosome stability.” Expert review of proteomics. U.S. National Library of Medicine, Oct. 2005. Web. 15 May 2017.
Image Courtesy:
1. “Nucleosome structure-2” By Nucleosome_structure.png: Richard Wheeler (Zephyris)derivative work: Rekymanto (talk) – Nucleosome_structure.png (CC BY-SA 3.0) via Commons Wikimedia