Previously, a seven-cluster pattern claiming to be a universal one in bacterial genomes has been reported. Keeping in mind the most popular theory of chloroplast origin, we checked whether a similar pattern is observed in chloroplast genomes. Surprisingly, eight cluster structure has been found, for chloroplasts. The pattern observed for chloroplasts differs rather significantly, from bacterial one, and from that latter observed for cyanobacteria. The structure is provided by clustering of the fragments of equal length isolated within a genome so that each fragment is converted in triplet frequency dictionary with non-overlapping triplets with no gaps in frame tiling. The points in 63-dimensional space were clustered due to elastic map technique. The eight cluster found in chloroplasts comprises the fragments of a genome bearing tRNA genes and exhibiting excessively high GC-content, in comparison to the entire genome. Chloroplasts exhibit very specific symmetry type in distribution of coding and non-coding fragments of a genome in the space of triplet frequencies: this is mirror symmetry. Cyanobacteria may have both mirror symmetry, and the rotational symmetry typical for other bacteria.

中文翻译：

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叶绿体基因组中惊人的对称簇。

以前，已经报道了声称在细菌基因组中通用的七簇模式。牢记最流行的叶绿体起源理论，我们检查了在叶绿体基因组中是否观察到相似的模式。令人惊讶的是，已经发现了用于叶绿体的八个簇结构。叶绿体观察到的模式与细菌观察到的模式明显不同，后者与蓝细菌观察到的模式明显不同。通过在基因组内分离等长片段的聚类来提供结构，从而使每个片段在三重态频率字典中转换为不重叠的三胞胎，且帧平铺没有间隙。63维空间中的点由于弹性贴图技术而聚类。与整个基因组相比，叶绿体中发现的八个簇包含携带tRNA基因的基因组片段，并且GC含量过高。叶绿体在三联体频率的空间中，在基因组的编码和非编码片段分布中表现出非常特定的对称类型：这是镜像对称。蓝细菌可能同时具有镜像对称性和其他细菌通常具有的旋转对称性。