Lauer J, Shen C K, Maniatis T
Cell. 1980 May;20(1):119-30. doi: 10.1016/0092-8674(80)90240-8.
We report the isolation of a cluster of four alpha-like globin genes from a bacteriophage lambda library of human DNA (Lawn et al., 1978). Analysis of the cloned DNA confirms the linkage arrangement of the two adult alpha-globin genes (alpha 1 and alpha 2) previously derived from genomic blotting experiments (Orkin, 1978) and identifies two additional closely linked alpha-like genes. The nucleotide sequence of a portion of each of these alpha-like genes was determined. One of these sequences is tentatively identified as an embryonic zeta-globin gene (zeta 1) by comparison with structural data derived from purified zeta-globin protein (J. Clegg, personal communication), while the other sequence cannot be matched with any known alpha-like polypeptide sequence (we designate this sequence phi alpha 1). Localization of the four alpha-like sequences on a restriction map of the gene cluster indicates that the genes have the same transcriptional orientation and are arranged in the order 5'-zeta 1-phi alpha 1-alpha 2-alpha 1-3'. Genomic blotting experiments identified a second, nonallelic zeta-like globin gene (phi 2) located 10-12 kb 5' to the cloned zeta-globin gene. Comparison of the locations of restriction sites within alpha 1 and alpha 2 and heteroduplex studies reveal extensive sequence homology within and flanking the two genes. The homologous sequences, which are interrupted by two blocks of nonhomology, span a region of approximately 4 kb. This extensive sequence homology between two genes which are thought to be the products of an ancient duplication event suggests the existence of a mechanism for sequence matching during evolution. One consequence of this arrangement of homologous sequences is the occurrence of two types of deletions in recombinant phage DNA during propagation in E. coli. The locations and sizes of the two types of deletions are indistinguishable from those of the two types of deletions associated with alpha-thalassemia 2 (Embury et al., 1979; Orkin et al., 1979; S. Embury et al., manuscript submitted). This information strongly suggests that the genetic disease is a consequence of unequal crossing over between homologous sequences within and/or surrounding the two adult alpha-globin genes.
我们报道了从人类DNA的噬菌体λ文库中分离出一组四个类α珠蛋白基因（Lawn等人，1978年）。对克隆DNA的分析证实了先前通过基因组印迹实验得出的两个成人α珠蛋白基因（α1和α2）的连锁排列（Orkin，1978年），并鉴定出另外两个紧密连锁的类α基因。测定了这些类α基因中每个基因一部分的核苷酸序列。通过与从纯化的ζ珠蛋白中获得的结构数据进行比较（J. Clegg，个人交流），其中一个序列被初步鉴定为胚胎ζ珠蛋白基因（ζ1），而另一个序列无法与任何已知的类α多肽序列匹配（我们将此序列命名为φα1）。这四个类α序列在基因簇的限制酶切图谱上的定位表明，这些基因具有相同的转录方向，并按5'-ζ1-φα1-α2-α1-3'的顺序排列。基因组印迹实验鉴定出第二个非等位的类ζ珠蛋白基因（φ2），位于克隆的ζ珠蛋白基因5'端10 - 12 kb处。α1和α2内限制酶切位点位置的比较以及异源双链体研究揭示了这两个基因内部和侧翼存在广泛的序列同源性。同源序列被两个非同源区域打断，跨度约为4 kb。这两个被认为是古老重复事件产物的基因之间广泛的序列同源性表明，在进化过程中存在一种序列匹配机制。同源序列这种排列的一个结果是，在大肠杆菌中繁殖期间，重组噬菌体DNA中出现了两种类型的缺失。这两种类型缺失的位置和大小与与α地中海贫血2相关的两种类型缺失的位置和大小无法区分（Embury等人，1979年；Orkin等人，1979年；S. Embury等人，手稿已提交）。这些信息强烈表明遗传疾病是两个成人α珠蛋白基因内部和/或周围同源序列之间不等交换的结果。
