A polyglutamine tract or polyQ tract is a portion of a protein consisting of a sequence of several glutamine units. A tract typically consists of about 10 to a few hundred such units.
A multitude of genes, in various eukaryotic species (including humans), contain a number of repetitions of the nucleotide triplet CAG or CAA. When the gene is translated into a protein, each of these triplets gives rise to a glutamine unit, resulting in a polyglutamine tract. Different alleles of such a gene often have different numbers of triplets since the highly repetitive sequence is prone to contraction and expansion.
Several inheritable neurodegenerative disorders, the polyglutamine diseases, occur if a mutation causes a polyglutamine tract in a specific gene to become too long. Important examples of polyglutamine diseases are spinocerebellar ataxia and Huntington's disease. It is believed that cells cannot properly dispose of proteins with overly long polyglutamine tracts, which over time leads to damage in nerve cells. The longer the polyglutamine tract, the earlier in life these diseases tends to appear.
Famous quotes containing the word tract:
“Every living language, like the perspiring bodies of living creatures, is in perpetual motion and alteration; some words go off, and become obsolete; others are taken in, and by degrees grow into common use; or the same word is inverted to a new sense or notion, which in tract of time makes an observable change in the air and features of a language, as age makes in the lines and mien of a face.”
—Richard Bentley (1662–1742)