Jellie A M, Tate W P, Trotman C N
Department of Biochemistry, University of Otago, Box 56, Dunedin, New Zealand.
J Mol Evol. 1996 Jun;42(6):641-7. doi: 10.1007/BF02338797.
The Artemia hemoglobin contains two subunits that are similar or different chains of nine globin domains. The domains are ancestrally related and are presumed to be derived from copies of an original single-domain parent gene. Since the gene copies have remained in the same environment for several hundred million years they provide an excellent model for the investigation of intron stability. The cDNA for one of the two types of nine-domain subunit (domains T1-T9) has been sequenced. Comparison with the corresponding genomic DNA reveals a total of 17 intradomain introns. Fourteen of the introns are in locations on the protein that are conventional in globins of other species. In eight of the nine domains an intron corresponds to the B helix, amino acid B12, following the second nucleotide (phase 2), and in six domains a G-helix intron is located between G6 and G7 (phase 0). The consistency of this pattern is supportive of the introns having been inherited from a single-domain parent gene. The remaining three introns are in unconventional locations. Two occur in the F helix, either in amino acid F3 (phase 1) in domain T3, or between F2 and F3 (phase 0) in domain T6. The two F introns strengthen an interpretation of intron inheritance since globin F introns are rare, and in domains T3 and T6 they replace rather than supplement the conventional G introns, as though displacement from G to F occurred before that part of the gene became duplicated. It is inferred that one of the F introns subsequently moved by one nucleotide. Similarly, the third unconventional intron location is the G intron in domain T4 which is in G6, phase 2, one nucleotide earlier than the other G introns. Domain T4 is also unusual in lacking a B intron. The pattern of introns in the Artemia globin gene supports a concept of general positional stability but the exceptions, where introns have moved out of reading frame, or have moved by several codons, or have been deleted, suggest that intron displacements can occur after inheritance from an ancient source.
卤虫血红蛋白包含两个亚基，它们是由九条珠蛋白结构域组成的相似或不同的链。这些结构域在进化上相关，据推测是由一个原始单结构域亲本基因的拷贝衍生而来。由于基因拷贝在相同环境中已存在数亿年，它们为研究内含子稳定性提供了一个绝佳模型。已对两种九结构域亚基之一（结构域T1 - T9）的cDNA进行了测序。与相应的基因组DNA比较后发现共有17个结构域内内含子。其中14个内含子位于其他物种珠蛋白中常见的蛋白质位置。在九个结构域中的八个中，一个内含子对应于B螺旋，氨基酸B12，位于第二个核苷酸之后（相位2），在六个结构域中，一个G螺旋内含子位于G6和G7之间（相位0）。这种模式的一致性支持这些内含子是从单结构域亲本基因遗传而来的观点。其余三个内含子位于非常规位置。两个出现在F螺旋中，要么在结构域T3的氨基酸F3处（相位1），要么在结构域T6的F2和F3之间（相位0）。这两个F内含子强化了内含子遗传的解释，因为珠蛋白F内含子很少见，并且在结构域T3和T6中它们取代而非补充常规的G内含子，就好像从G到F的位移发生在该基因的那部分被复制之前。据推测，其中一个F内含子随后移动了一个核苷酸。同样，第三个非常规内含子位置是结构域T4中的G内含子，它在G6处，相位2，比其他G内含子早一个核苷酸。结构域T4也很特别，它缺少一个B内含子。卤虫珠蛋白基因中的内含子模式支持一般位置稳定性的概念，但存在一些例外情况，即内含子移出阅读框、移动了几个密码子或被删除，这表明内含子位移可能在从古老来源遗传之后发生。
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