engleski

Functional elements in satellite DNAs

Satellite DNAs are highly repetitive sequences located in heterochromatic regions of eukaryotic chromosomes. They are usually characterized by rapid evolution of sequence and copy number what leads to their preservation among a limited number of closely related species. Despite such a high turnover satellite DNAs represent main centromere building element strongly associated with a number of proteins forming unique centromeric chromatin. In addition, some satellite DNA transcripts in the form of small interfering RNAs participate in the epigenetic process of chromatin modulation and heterochromatin establishment. Our recent data obtained by studying satellite DNAs of the coleopteran genus Palorus indicate that evolution of satellite sequence is not only driven by stochastic processes as previously proposed, but is influenced by selective constraints. These conclusions are based on extreme interspecific conservation and wide distribution of Palorus satellite sequences among species separated for long evolutionary periods. Their transcriptional activity in the form of multiple transcripts deriving from both DNA strands with approximate size between 5 kb and 1 kb is detected. The transcripts contain poly(A) tails and are present in cytoplasm. Major transcription initiation sites are determined and putative RNA polymerase II promoters are mapped within the satellite repeats. The transcripts are detected in all developmental stages but are the most abundant in adults, indicating their developmental regulation. Since we were not able to detect siRNAs homologous to satellite repeats, it could be proposed that longer transcripts play a role in heterochromatin formation.

satellite DNA; transcription; noncoding RNA

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