Minisatellite

A minisatellite is a tract of repetitive DNA in which certain DNA motifs (ranging in length from 10–60 base pairs) are typically repeated 5-50 times. Minisatellites occur at more than 1,000 locations in the human genome and they are notable for their high mutation rate and high diversity in the population. Minisatellites are prominent in the centromeres and telomeres of chromosomes, the latter protecting the chromosomes from damage. The name 'satellite' refers to the early observation that centrifugation of genomic DNA in a test tube separates a prominent layer of bulk DNA from accompanying 'satellite' layers of repetitive DNA. Minisatellites are small sequences of DNA that do not encode proteins but appear throughout the genome hundreds of times, with many repeated copies lying next to each other. A minisatellite is a tract of repetitive DNA in which certain DNA motifs (ranging in length from 10–60 base pairs) are typically repeated 5-50 times. Minisatellites occur at more than 1,000 locations in the human genome and they are notable for their high mutation rate and high diversity in the population. Minisatellites are prominent in the centromeres and telomeres of chromosomes, the latter protecting the chromosomes from damage. The name 'satellite' refers to the early observation that centrifugation of genomic DNA in a test tube separates a prominent layer of bulk DNA from accompanying 'satellite' layers of repetitive DNA. Minisatellites are small sequences of DNA that do not encode proteins but appear throughout the genome hundreds of times, with many repeated copies lying next to each other. Minisatellites and their shorter cousins, the microsatellites, together are classified as VNTR (variable number of tandem repeats) DNA. Confusingly, minisatellites are often referred to as VNTRs, and microsatellites are often referred to as short tandem repeats (STRs) or simple sequence repeats (SSRs). Minisatellites consist of repetitive, generally GC-rich, motifs that range in length from 10 to over 100 base pairs. These variant repeats are tandemly intermingled. Some minisatellites contain a central sequence (or 'core unit') of nucleobases “GGGCAGGANG” (where N can be any base) or more generally consist of sequence motifs of purines (Adenine (A) and Guanine (G)) and pyrimidines (Cytosine (C) and Thymine (T)). Hypervariable minisatellites have core units 9–64 bp long and are found mainly at the centromeric regions. In humans, 90% of minisatellites are found at the sub-telomeric region of chromosomes. The human telomere sequence itself is a tandem repeat: TTAGGG TTAGGG TTAGGG … Minisatellites have been implicated as regulators of gene expression (e.g. at levels of transcription, alternative splicing, or imprint control). They are generally non-coding DNA but sometimes are part of possible genes.