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Mobile DNA  2010 

Extrachromosomal circles of satellite repeats and 5S ribosomal DNA in human cells

DOI: 10.1186/1759-8753-1-11

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Abstract:

Here we report the occurrence of eccDNA in every tested human cell line. It has heterogeneous mass ranging from less than 2 kb to over 20 kb. We describe eccDNA homologous to human alpha satellite and the SstI mega satellite. Moreover, we show, for the first time, circular multimers of the human 5S ribosomal DNA (rDNA), similar to previous findings in Drosophila and plants. We further demonstrate structures that correspond to intermediates of rolling circle replication, which emerge from the circular multimers of 5S rDNA and SstI satellite.These findings, and previous reports, support the general notion that every chromosomal tandem repeat is prone to generate eccDNA in eukryoric organisms including humans. They suggest the possible involvement of eccDNA in the length variability observed in arrays of tandem repeats. The implications of eccDNA on genome biology may include mechanisms of centromere evolution, concerted evolution and homogenization of tandem repeats and genomic plasticity.The genome of eukaryotes has been considered for a long time to be relatively stable. However, various phenomena have been described which exhibit the plasticity of the genome and occur during the normal lifespan of the organism. An intriguing manifestation of the plasticity of the eukaryotic genome is the occurrence of extrachromosomal circular DNA (eccDNA) - also termed spcDNA (small poly-dispersed circular DNA). While the population of extrachromosomal circles may include intermediates of mobile elements or viral genomes, here we refer to the circular molecules as eccDNA which are derived primarily from chromosomal repetitive sequences that do not appear to harbour an intrinsic 'jumping' or excision mechanism mediated by specific sequences.eccDNA is ubiquitous in eukaryotic genomes and has been detected in every organism tested, including human tissues and cultured cells [1,2]. eccDNA has been reported in various human cells and was characterized mainly by electron microscopy or c

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