Banks G K, Robinson A S, Kwiatowski J, Ayala F J, Scott M J, Kriticou D
Department of Plant Science, University of Arizona, Tucson 85721, USA.
Genetics. 1995 Jun;140(2):697-702. doi: 10.1093/genetics/140.2.697.
We report the first case of two Cu/Zn Sod genes (ccSod1 and ccSod2) that have been cloned and sequenced from an insect, the medfly, Ceratitis capitata. Biochemical evidence suggested the presence of two Sod genes in the medfly. The two genes are isolated using different molecular strategies: ccSod1 via cross-hybridization to a genomic library using a heterologous probe and ccSod2 from cDNA using a homologous probe generated by PCR. Sequence analysis shows that ccSod1 and ccSod2 are different genes. The inferred amino sequences show that all essential residues of the active site are strictly conserved, which suggests both genes encode functional Cu/Zn superoxide dismutase (SOD). Phylogenetic analysis by the maximum parsimony method with bootstrap resampling of previously known Cu/Zn SOD reveals two monophyletic groups, vertebrates and insects. The position of ccSOD2 in this phylogeny is undefined with respect to dipteran ccSOD1, vertebrate, plant, fungal, and extracellular Cu/Zn SOD, which suggests that the duplication detected in Ceratitis is ancient, perhaps as old as the origins of the arthropod phylum in the Cambrian more than 500 million years ago. In situ hybridization to polytene chromosomes places the genes on different chromosomes, which is consistent with an ancient gene duplication.
我们报道了首例从一种昆虫——地中海实蝇（Ceratitis capitata）中克隆并测序出两个铜/锌超氧化物歧化酶基因（ccSod1和ccSod2）的案例。生化证据表明地中海实蝇中存在两个超氧化物歧化酶基因。这两个基因是通过不同的分子策略分离得到的：ccSod1是利用异源探针与基因组文库进行交叉杂交获得，而ccSod2则是从利用PCR产生的同源探针从cDNA中分离得到。序列分析表明ccSod1和ccSod2是不同的基因。推断的氨基酸序列显示活性位点的所有必需残基都严格保守，这表明这两个基因都编码功能性的铜/锌超氧化物歧化酶（SOD）。通过最大简约法对先前已知的铜/锌超氧化物歧化酶进行自展重抽样的系统发育分析揭示了两个单系类群，即脊椎动物和昆虫。在这个系统发育中，ccSOD2相对于双翅目ccSOD1、脊椎动物、植物、真菌和细胞外铜/锌超氧化物歧化酶的位置不明确，这表明在地中海实蝇中检测到的基因复制是古老的，可能与5亿多年前寒武纪节肢动物门的起源一样古老。对多线染色体进行原位杂交将这些基因定位在不同的染色体上，这与古老的基因复制是一致的。
