Satellite DNA

Satellite DNA comprises very large arrays of tandemly repeated noncoding DNA, usually megabases in size, which form the major structural constituent of hetero-chromatin, a tightly packaged condensed state of transcriptionally suppressed DNA. Satellite DNA is the main component of functional centromeres, as well as het-erochromatin in pericentromeric and telomeric regions, and in the short arms of the acrocentric chromosomes (chromosomes 13, 14, 15, 21, and 22) (Charlesworth et al. 1994; Schueler et al. 2001). Satellite DNA is recognized across eukaryotic genomes, in some species such as the kangaroo rat Dipodomys ordii comprising half of the total genomic DNA content (Hatch and Mazrimas 1974). The technical challenges of sequencing and analysing such large repetitive DNA sequences has meant only limited coverage in genome assemblies, such that our understanding of the precise structure, organization, and functional importance of satellite DNA remains relatively incomplete. The unusual structure of satellite DNA may be the preferred state at centromeres and flanking regions. The specific composition of satellite DNA is variable and typically species-specific. Concerted evolution is thought to maintain sequence homogeneity of species-specific satellite arrays but allow for the rapid change in sequence or composition of repeats required during evolution (Plohl et al. 2008).

Early work using density gradient centrifugation resolved that specific 'satellite' bands could be separated from the bulk of genomic DNA due to differences in nucleotide content: three major classes were noted with different satellite subfamilies (Corneo et al. 1968; Prosser et al. 1981). Other types of satellite DNA cannot be easily separated by centrifugation and were initially identified by particular restriction enzymes recognizing motifs in the basic repeat unit. Satellite DNA varies in the nucleotide sequences involved, the complexity of the repeat structure, and genomic abundance. Many satellite monomers are in the size range 150-180 bp, the DNA length required to wrap around a nucleosome, or 300-360 bp (sufficient for two nucleosomes). It is now known that satellite DNA repeats include alpha satellite DNA (tandem repeats of a 171 bp monomer), beta satellite DNA (a 68 bp repeat), satellite family 1 DNA (AT rich with repeat units from 25 to 48 bp in length), and satellites families 2 and 3 (with much simpler 5 bp repeats). When it was first identified, satellite DNA was recognized to not encode specific proteins and was initially regarded

Satellite Dna

Figure 7.1 Schematic representation of tandemly repeated DNA. Satellite DNA covers very large regions of the genome, for example 171 bp monomers of alpha satellite DNA organized into units several hundred base pairs in length that may be repeated hundreds or thousands of times. A polymorphic minisatellite is shown comprised of between six and ten repeats of an ATGCCTATTGG sequence. A tetranucleotide (ATGG)n and dinucleotide (CA)n microsatellite are also shown.

Figure 7.1 Schematic representation of tandemly repeated DNA. Satellite DNA covers very large regions of the genome, for example 171 bp monomers of alpha satellite DNA organized into units several hundred base pairs in length that may be repeated hundreds or thousands of times. A polymorphic minisatellite is shown comprised of between six and ten repeats of an ATGCCTATTGG sequence. A tetranucleotide (ATGG)n and dinucleotide (CA)n microsatellite are also shown.

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Responses

  • Aurora
    What are alpha and beta repeat repeat?
    3 months ago

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