Scaffold attachment region

The term 'S/MAR' (scaffold/matrix attachment region), otherwise called 'SAR' (scaffold-attachment region), or 'MAR' (matrix-associated region), are sequences in the DNA of eukaryotic chromosomes where the nuclear matrix attaches. As architectural DNA components that organize the genome of eukaryotes into functional units within the cell nucleus, S/MARs mediate structural organization of the chromatin within the nucleus. These elements constitute anchor points of the DNA for the chromatin scaffold and serve to organize the chromatin into structural domains. Studies on individual genes led to the conclusion that the dynamic and complex organization of the chromatin mediated by S/MAR elements plays an important role in the regulation of gene expression.

It has been known for many years that a polymer meshwork, a so-called "nuclear matrix" or "nuclear-scaffold" is an essential component of eukaryotic nuclei. This nuclear skeleton acts as a dynamic support for many specialized events concerning the readout a spread of genetic information (see below).

S/MARs map to non-random locations in the genome. They occur at the flanks of transcribed regions, in 5´-introns, and also at gene breakpoint cluster regions (BCRs). Being association points for common nuclear structural proteins S/MARs are required for authentic and efficient chromosomal replication and transcription, for recombination and chromosome condensation. S/MARs do not have an obvious consensus sequence. Although prototype elements consist of AT-rich regions several hundred base pairs in length, the overall base composition is definitely not the primary determinant of their activity. Instead, their function requires a pattern of "AT-patches" that confer the propensity for local strand unpairing under torsional strain.

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