Jabs E W, Persico M G
Am J Hum Genet. 1987 Sep;41(3):374-90.
The alphoid DNA family is composed of tandemly repeated sequences whose organization is chromosome specific. Under stringent conditions of hybridization, subsets of these sequences localize specifically to the centromeric region of a given chromosome. The alphoid clone, 308 (D6Z1), is a 3-kb BamHI DNA fragment that is repeated at the centromere of chromosome 6. Sequences homologous to 308 are organized as 2-kb BamHI repeats on X. We used 308 to screen a 2-kb BamHI genomic library and obtained the cloned homologue, XC, which hybridizes, in situ, to the centromere of X. These probes provide a means of analyzing the centromeric region on two different human chromosomes. The complete nucleotide sequence of 308 shows that it is composed of 20 variant 173-bp repeats. The organization of the 173-bp monomers is not a repetitious but a symmetric pattern, and an inversion is present. The chromosome specificity of 308 to chromosome 6 is determined by the entire 3-kb sequence and not by an amplified 173-bp monomer, because the divergence among the 173-bp units on chromosome 6 is as great as that between monomers on chromosomes 6 and X. Therefore, the organization of monomers is specific for a chromosome, and the monomers themselves are not specific. Analysis of the sequence data from these two alphoid sequences and other published sequences shows that some chromosomes have sequences that are more homologous than others. These subsets of alphoid sequences reflect the latters' chromosomal distribution and evolution. By using probes 308 and XC, we found that alphoid repeats from specific chromosomes are similar in that there is no evidence for their transcription in lymphoblasts and fibroblasts, and we demonstrated the possibility that all of these sequences are late replicating.
α卫星DNA家族由串联重复序列组成，其序列组织具有染色体特异性。在严格的杂交条件下，这些序列的亚群特异性定位于特定染色体的着丝粒区域。α卫星克隆308（D6Z1）是一个3 kb的BamHI DNA片段，在6号染色体的着丝粒处重复。与308同源的序列在X染色体上以2 kb的BamHI重复序列形式存在。我们用308筛选了一个2 kb的BamHI基因组文库，获得了克隆的同源物XC，它在原位与X染色体的着丝粒杂交。这些探针为分析两条不同人类染色体的着丝粒区域提供了一种方法。308的完整核苷酸序列表明它由20个173 bp的可变重复序列组成。173 bp单体的组织不是重复模式而是对称模式，并且存在一个倒位。308对6号染色体的特异性是由整个3 kb序列决定的，而不是由一个扩增的173 bp单体决定的，因为6号染色体上173 bp单元之间的差异与6号和X染色体上单体之间的差异一样大。因此，单体的组织对一条染色体是特异性的，而单体本身不是特异性的。对这两个α卫星序列和其他已发表序列的序列数据进行分析表明，一些染色体的序列比其他染色体的序列具有更高的同源性。这些α卫星序列亚群反映了它们的染色体分布和进化。通过使用探针308和XC，我们发现来自特定染色体的α卫星重复序列相似之处在于，没有证据表明它们在淋巴母细胞和成纤维细胞中进行转录，并且我们证明了所有这些序列都可能是晚期复制的。
