Wevrick R, Willard V P, Willard H F
Department of Genetics, Stanford University, California 94305.
Genomics. 1992 Dec;14(4):912-23. doi: 10.1016/s0888-7543(05)80112-0.
The centromeric regions of human chromosomes contain long tracts of tandemly repeated DNA, of which the most extensively characterized is alpha satellite. In a screen for additional centromeric DNA sequences, four phage clones were obtained which contain alpha satellite as well as other sequences not usually found associated with tandemly repeated alpha satellite DNA, including L1 repetitive elements, an Alu element, and a novel AT-rich repeated sequence. The alpha satellite DNA contained within these clones does not demonstrate the higher-order repeat structure typical of tandemly repeated alpha satellite. Two of the clones contain inversions; instead of the usual head-to-tail arrangement of alpha satellite monomers, the direction of the monomers changes partway through each clone. The presence of both inversions was confirmed in human genomic DNA by polymerase chain reaction amplification of the inverted regions. One phage clone contains a junction between alpha satellite DNA and a novel low-copy repeated sequence. The junction between the two types of DNA is abrupt and the junction sequence is characterized by the presence of runs of A's and T's, yielding an overall base composition of 65% AT with local areas > 80% AT. The AT-rich sequence is found in multiple copies on chromosome 7 and homologous sequences are found in (peri)centromeric locations on other human chromosomes, including chromosomes 1, 2, and 16. As such, the AT-rich sequence adjacent to alpha satellite DNA provides a tool for the further study of the DNA from this region of the chromosome. The phage clones examined are located within the same 3.3-Mb SstII restriction fragment on chromosome 7 as the two previously described alpha satellite arrays, D7Z1 and D7Z2. These new clones demonstrate that centromeric repetitive DNA, at least on chromosome 7, may be more heterogeneous in composition and organization than had previously been thought.
人类染色体的着丝粒区域包含长片段串联重复DNA，其中特征最为广泛的是α卫星DNA。在一项寻找其他着丝粒DNA序列的筛选中，获得了四个噬菌体克隆，它们包含α卫星DNA以及其他通常未发现与串联重复α卫星DNA相关的序列，包括L1重复元件、一个Alu元件和一个新的富含AT的重复序列。这些克隆中包含的α卫星DNA并未表现出串联重复α卫星典型的高阶重复结构。其中两个克隆包含倒位；α卫星单体不是通常的头对头排列方式，而是在每个克隆中途单体方向发生改变。通过对倒位区域进行聚合酶链反应扩增，在人类基因组DNA中证实了这两个倒位的存在。一个噬菌体克隆包含α卫星DNA与一个新的低拷贝重复序列之间的连接。两种DNA之间的连接是突然的，连接序列的特征是存在一连串的A和T，整体碱基组成中AT占65%，局部区域AT含量>80%。富含AT的序列在7号染色体上有多个拷贝，在其他人类染色体（包括1号、2号和16号染色体）的（近）着丝粒位置也发现了同源序列。因此，与α卫星DNA相邻的富含AT序列为进一步研究该染色体区域的DNA提供了一个工具。所检测的噬菌体克隆与之前描述的两个α卫星阵列D7Z1和D7Z2位于7号染色体上同一个3.3 Mb的SstII限制片段内。这些新克隆表明，着丝粒重复DNA，至少在7号染色体上，其组成和组织可能比之前认为的更加异质。
