Department of Biochemistry, University of Aberdeen, Marischal College, Aberdeen AB9 1AS, UK.
EMBO J. 1985 Dec 16;4(13A):3557-62. doi: 10.1002/j.1460-2075.1985.tb04117.x.
A family of long, highly-repetitive sequences, referred to previously as ;HpaII-repeats', dominates the genome of the eukaryotic slime mould Physarum polycephalum. These sequences are found exclusively in scrambled clusters. They account for about one-half of the total complement of repetitive DNA in Physarum, and represent the major sequence component found in hypermethylated, 20-50 kb segments of Physarum genomic DNA that fail to be cleaved using the restriction endonuclease HpaII. The structure of this abundant repetitive element was investigated by analysing cloned segments derived from the hypermethylated genomic DNA compartment. We show that the ;HpaII-repeat' forms part of a larger repetitive DNA structure, approximately 8.6 kb in length, with several structural features in common with recognised eukaryotic transposable genetic elements. Scrambled clusters of the sequence probably arise as a result of transposition-like events, during which the element preferentially recombines in either orientation with target sites located in other copies of the same repeated sequence. The target sites for transposition/recombination are not related in sequence but in all cases studied they are potentially capable of promoting the formation of small ;cruciforms' or ;Z-DNA' structures which might be recognised during the recombination process.
一个长的、高度重复的序列家族，以前称为“HpaII 重复序列”，在真核黏菌 Physarum polycephalum 的基因组中占主导地位。这些序列仅存在于乱序簇中。它们约占 Physarum 总重复 DNA 的一半，代表了在 Physarum 基因组 DNA 中未被限制性内切酶 HpaII 切割的高度甲基化、20-50kb 片段中主要的序列成分。通过分析来自超甲基化基因组 DNA 区的克隆片段，研究了这种丰富的重复元件的结构。我们表明，“HpaII 重复序列”是一个更大的重复 DNA 结构的一部分，大约 8.6kb 长，与公认的真核可移动遗传元件具有几个共同的结构特征。序列的乱序簇可能是转座样事件的结果，在此过程中，该元件优先以任一方向与位于同一重复序列的其他拷贝中的靶位点进行重组。转座/重组的靶位点在序列上没有关系，但在所研究的所有情况下，它们都有可能促进小“十字形”或“Z-DNA”结构的形成，这些结构可能在重组过程中被识别。
