engleski

Functional elements in non-coding satellite DNAs

Satellite DNAs are tandemly repeated sequences that are present as long uninterrupted arrays in genetically silent heterochromatic regions. Despite their structural divergence they are major constituents of heterochromatin and act as a centromere-building element in association with a number of proteins. Satellite DNAs represent a fast-evolving portion of the eukaryotic genome proposed to drive evolution of centromere. Evidence is accumulating on the functional significance of satellite DNA sequences, in particular the uneven distribution of mutations within satellite repeats that results in conserved and variable segments and the extreme sequence conservation and evolutionary preservation of some satellites. Recent results indicate certain structural constraints on satellite DNA sequence, probably related to their interaction with proteins involved in the establishment of specific chromatin structures. The evolutionary persistence and high sequence conservation of some satellites are consistent with the hypothesis that satellite DNA plays a regulatory role in eukaryotic organisms. Widespread transcriptional activity together with the presence of active promoters and binding sites for transcription factors, found within some satellites, further support their functional importance. Although the role of most transcripts is not known, some act as precursors of small interfering RNAs (siRNAs), which are now recognized as having an important role in epigenetic chromatin modulation. Others exhibit ribozyme activity, whereas human satellite III transcripts are involved in the recruitment of splicing factors regulating in this way cellular response to stress. These examples suggest an active role for satellite transcripts in multiple regulatory layers from chromatin modulation, transcription, RNA maturation to translation. As the transcription of most satellites is either developmentally and temporally regulated or restricted to particular tissues and organs, it is plausible that the transcripts are responsible for fine-tuning gene expression. However, the precise biochemical mechanisms of action of different satellites and their transcripts still need to be determined.

satellite DNA; heterochromatin; noncoding RNA

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