engleski

Changes and persistence in the evolution of satellite DNAs

Highly abundant DNA sequences repeated in tandem, called satellite DNAs (satDNA) underlie heterochromatic genome compartments in all eukaryotes, building sometimes over 50% of genomic DNA. Large differences in satDNA sequences observed among species are traditionally explained as a consequence of rapid accumulation of mutations in reproductively isolated lines, due to the lack of selective pressure. The library model explains the origin of these differences by amplifications-contractions in a set of satDNA families shared by a group of organisms, a phenomenon which does not necessarily include satDNA sequence alterations. Indeed, several studied satDNAs indicate conservation of their sequences during extremely long evolutionary periods. Reluctance to sequence changes can be a fundamental feature of at least some tandem repeats, as a consequence of mechanisms homogenizing satDNA monomers in a conservative way, i.e. preferentially preventing accumulation and spread of new changes in the repetitive family in absence of any constraints. If so, tandem repeats may represent an organizational form able to make DNA sequence conserved through the evolution. Nevertheless, genomic composition of tandem repeats coexisting in the genome can be changed rapidly through the copy number alterations. This dual character of satDNAs, to persist and change rapidly during evolution, in heterochromatic chromosomal segments may guarantee long-term stability of interactions involved in some basic functions, such as in and around centromeres, where rapid adjustments of DNA-protein interactions might be crucial for chromosomal integrity and function.

Satellite DNA; concerted evolution; library model; sequence variability

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