BACKGROUND Satellites or tandem repeats are very abundant in many eukaryotic genomes. Occasionally they have been reported to be present in some prokaryotes, but to our knowledge there is no general comparative study on their occurrence. For this reason we present here an overview of the distribution and properties of satellites in a set of representative species. Our results provide novel insights into the evolutionary relationship between eukaryotes, Archaea and Bacteria. RESULTS We have searched all possible satellites present in the NCBI reference group of genomes in Archaea (142 species) and in Bacteria (119 species), detecting 2735 satellites in Archaea and 1067 in Bacteria. We have found that the distribution of satellites is very variable in different organisms. The archaeal Methanosarcina class stands out for the large amount of satellites in their genomes. Satellites from a few species have similar characteristics to those in eukaryotes, but most species have very few satellites: only 21 species in Archaea and 18 in Bacteria have more than 4 satellites/Mb. The distribution of satellites in these species is reminiscent of what is found in eukaryotes, but we find two significant differences: most satellites have a short length and many of them correspond to segments of genes coding for amino acid repeats. Transposition of non-coding satellites throughout the genome occurs rarely: only in the bacteria Leptospira interrogans and the archaea Methanocella conradii we have detected satellite families of transposed satellites with long repeats. CONCLUSIONS Our results demonstrate that the presence of satellites in the genome is not an exclusive feature of eukaryotes. We have described a few prokaryotes which do contain satellites. We present a discussion on their eventual evolutionary significance.

中文翻译：

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原核生物世界中的卫星。

背景技术在许多真核基因组中，卫星或串联重复序列非常丰富。据报道它们偶尔存在于某些原核生物中，但据我们所知，尚无关于它们发生的一般比较研究。因此，我们在此概述一组代表性物种中卫星的分布和特性。我们的结果为真核生物，古细菌和细菌之间的进化关系提供了新颖的见解。结果我们搜索了古细菌（142种）和细菌（119种）的NCBI参考基因组中存在的所有可能的卫星，检测到古细菌中的2735颗卫星和细菌中的1067颗卫星。我们发现，卫星的分布在不同的生物中变化很大。古细菌甲烷八叠球菌类在其基因组中的大量卫星中脱颖而出。少数物种的卫星具有与真核生物类似的特征，但是大多数物种的卫星却很少：古细菌中只有21种，细菌中只有18种具有每Mb 4颗以上的卫星。这些物种中卫星的分布让人想起在真核生物中的分布，但我们发现两个明显的差异：大多数卫星的长度较短，其中许多对应于编码氨基酸重复序列的基因片段。非编码卫星在整个基因组中的移位很少发生：仅在问号钩端螺旋体和古生甲烷球菌中，我们才发现了长重复序列的转座卫星的卫星家族。结论我们的结果表明，基因组中卫星的存在不是真核生物的专有特征。我们已经描述了一些确实包含卫星的原核生物。我们对它们最终的进化意义进行了讨论。