Mitochondrially encoded tRNA valine also known as MT-TV is a transfer RNA which in humans is encoded by the mitochondrial ''MT-TV''

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

Structure

The ''MT-TV'' gene is located on the

p arm In genetics, a locus (plural loci) is a specific, fixed position on a chromosome where a particular gene or genetic marker is located. Each chromosome carries many genes, with each gene occupying a different position or locus; in humans, the total ...

of the non-nuclear mitochondrial DNA at position 12 and it spans 69 base pairs. The structure of a

tRNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes), that serves as the physical link between the mRNA and the amino ...

molecule is a distinctive folded structure which contains three hairpin loops and resembles a three-leafed

clover Clover or trefoil are common names for plants of the genus ''Trifolium'' (from Latin ''tres'' 'three' + ''folium'' 'leaf'), consisting of about 300 species of flowering plants in the legume or pea family Fabaceae originating in Europe. The genus ...

Function

MT-TV is a small 69 nucleotide

RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...

( human mitochondrial map position 1602-1670) that transfers the amino acid

valine Valine (symbol Val or V) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α- amino group (which is in the protonated −NH3+ form under biological conditions), an α- carboxylic acid group (which is in the deprotona ...

to a growing polypeptide chain at the ribosome site of

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

synthesis during

translation Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...

. In animals, more specifically vertebrates, MT-tRNA^Val performs an integral structural role for the mitoribosome by filling in the position of a missing 5S mitoribosomal RNA.

Clinical significance

Mutations in ''MT-TV'' which impair oxidate phosphorylation result in mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). MELAS is a rare mitochondrial disorder known to affect many parts of the body, especially the

nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes ...

and the

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a ve ...

. Symptoms of MELAS include recurrent severe

headaches Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a result ...

, muscle weakness ( myopathy),

hearing loss Hearing loss is a partial or total inability to hear. Hearing loss may be present at birth or acquired at any time afterwards. Hearing loss may occur in one or both ears. In children, hearing problems can affect the ability to acquire spoken ...

, stroke-like episodes with a loss of

consciousness Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...

seizures An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much of the body with l ...

, and other problems affecting the

. Two specific mutations of 1642G>A and 1644G>A have been found to result in the disease. Changes in the gene have also been associated with

Leigh's syndrome Leigh syndrome (also called Leigh disease and subacute necrotizing encephalomyelopathy) is an inherited neurometabolic disorder that affects the central nervous system. It is named after Archibald Denis Leigh, a British neuropsychiatrist who fir ...

, a progressive brain disorder characterized by

vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Vomiting can be the result of ailments like food poisoning, gastroenteri ...

, delayed development, muscle weakness, problems with movement, heart disease,

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...

problems, and difficulty breathing. Symptoms typically appear in infancy or early

childhood A child (plural, : children) is a human being between the stages of childbirth, birth and puberty, or between the Development of the human body, developmental period of infancy and puberty. The legal definition of ''child'' generally refers ...

. A 1624C>T mutation has been linked to this disease. Other clinical manifestations associated with ''MT-TV'' mutations have included recurrent

migraine headaches Migraine (, ) is a common neurological disorder characterized by recurrent headaches. Typically, the associated headache affects one side of the head, is pulsating in nature, may be moderate to severe in intensity, and could last from a few hou ...

, muscle weakness and poor coordination,

learning disabilities Learning disability, learning disorder, or learning difficulty (British English) is a condition in the brain that causes difficulties comprehending or processing information and can be caused by several different factors. Given the "difficult ...

dementia Dementia is a disorder which manifests as a set of related symptoms, which usually surfaces when the brain is damaged by injury or disease. The symptoms involve progressive impairments in memory, thinking, and behavior, which negatively affe ...

, and more. It has not been found why such mutations cause symptoms of these diseases. A 1606A>G mutation resulted in

ataxia Ataxia is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in eye movements. Ataxia is a clinical manifestation indicating dysfunction of ...

accompanied by progressive seizures, mental deterioration, and hearing loss. Cardiomyopathy, which weakens and enlarges the heart muscle, has also been reported in a small number of affected individuals.

References

External links

GeneReviews/NCBI/NIH/UW entry on Mitochondrial DNA-Associated Leigh Syndrome and NARP
{{NLM content