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Reviewed April 2014

What is the official name of the MT-CYB gene?

The official name of this gene is “mitochondrially encoded cytochrome b.”

MT-CYB is the gene's official symbol. The MT-CYB gene is also known by other names, listed below.

Read more about gene names and symbols on the About page.

What is the normal function of the MT-CYB gene?

The MT-CYB gene provides instructions for making a protein called cytochrome b. This protein plays a key role in structures called mitochondria, which convert the energy from food into a form that cells can use. Cytochrome b is one of 11 components of a group of proteins called complex III. In mitochondria, complex III performs one step of a process known as oxidative phosphorylation, in which oxygen and simple sugars are used to create adenosine triphosphate (ATP), the cell's main energy source. During oxidative phosphorylation, the protein complexes, including complex III, drive the production of ATP through a step-by-step transfer of negatively charged particles called electrons. Cytochrome b is involved in the transfer of these particles through complex III.

Although most DNA is packaged in chromosomes within the nucleus (nuclear DNA), mitochondria also have a small amount of their own DNA, called mitochondrial DNA (mtDNA). This type of DNA contains many genes essential for normal mitochondrial function. Cytochrome b is the only component of complex III that is produced from a gene found in mitochondrial DNA.

Does the MT-CYB gene share characteristics with other genes?

The MT-CYB gene belongs to a family of genes called CYB (cytochrome b). It also belongs to a family of genes called mitochondrial respiratory chain complex (mitochondrial respiratory chain complex).

A gene family is a group of genes that share important characteristics. Classifying individual genes into families helps researchers describe how genes are related to each other. For more information, see What are gene families? in the Handbook.

How are changes in the MT-CYB gene related to health conditions?

mitochondrial complex III deficiency - caused by mutations in the MT-CYB gene

Mutations in the MT-CYB gene can cause mitochondrial complex III deficiency. When caused by mutations in this gene, the condition is usually characterized by muscle weakness (myopathy) and pain, especially during exercise (exercise intolerance). More severely affected individuals can have problems with other body systems, including the liver, kidneys, heart, and brain.

Most MT-CYB gene mutations that cause mitochondrial complex III deficiency change single protein building blocks (amino acids) in the cytochrome b protein or lead to an abnormally short protein. These cytochrome b alterations impair the formation of complex III, severely reducing the complex's activity and oxidative phosphorylation. Researchers believe that impaired oxidative phosphorylation can lead to cell death by reducing the amount of energy available in the cell. It is thought that tissues that require a lot of energy, such as those in the muscles, brain, heart, liver, and kidneys, are most affected by a reduction in oxidative phosphorylation. Damage to these tissues and organs leads to the various features of mitochondrial complex III deficiency.

The location of the MT-CYB gene in mitochondrial DNA (mtDNA) may help explain why some people have more severe features of the condition than others. Most of the body's cells contain thousands of mitochondria, each with one or more copies of mitochondrial DNA. These cells can have a mix of mitochondria containing mutated and unmutated DNA (heteroplasmy). The severity of mitochondrial complex III deficiency caused by MT-CYB gene mutations is thought to be associated with the percentage of mitochondria with the mitochondrial DNA mutation. In most people with MT-CYB-related mitochondrial complex III deficiency, the percentage of mutated mitochondrial DNA is highest in the skeletal muscles, which explains the finding of myopathy in these individuals. It is unclear why the mutation is most prevalent in muscle tissue.

Where is the MT-CYB gene located?

The MT-CYB gene is located in mitochondrial DNA.

Molecular Location in mitochondrial DNA: base pairs 14,747 to 15,887

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBIThis link leads to a site outside Genetics Home Reference.)

Overview of gene located on mitochondrial DNA Close-up of gene located on mitochondrial DNA

Where can I find additional information about MT-CYB?

You and your healthcare professional may find the following resources about MT-CYB helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the MT-CYB gene or gene products?

  • COB
  • CYTB
  • cytochrome b
  • cytochrome b (mitochondrion) [Homo sapiens]
  • UQCR3

Where can I find general information about genes?

The Handbook provides basic information about genetics in clear language.

These links provide additional genetics resources that may be useful.

What glossary definitions help with understanding MT-CYB?

acids ; adenosine triphosphate ; ATP ; cell ; charged particles ; coenzyme Q ; deficiency ; DNA ; electron ; gene ; heteroplasmy ; mitochondria ; mutation ; nucleus ; oxidative phosphorylation ; oxidoreductase ; oxygen ; phosphorylation ; protein ; tissue

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.

See also Understanding Medical Terminology.

References (5 links)


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.

Reviewed: April 2014
Published: February 8, 2016