Spieth J, Nettleton M, Zucker-Aprison E, Lea K, Blumenthal T
Department of Biology, Indiana University, Bloomington 47405.
J Mol Evol. 1991 May;32(5):429-38. doi: 10.1007/BF02101283.
Caenorhabditis elegans vitellogenins are encoded by a family of six genes, one of which, vit-5, has been previously sequenced and shown to be surprisingly closely related to the vertebrate vitellogenin genes. Here we report an alignment of the amino acid sequences of vitellogenins from frog and chicken with those from three C. elegans genes: vit-5 and two newly sequenced genes, vit-2 and vit-6. The four introns of vit-6 are all in different places from the four introns of vit-5, but three of these eight positions are identical or close to intron locations in the vertebrate vitellogenin genes. The encoded polypeptides have diverged from one another sufficiently to allow us to draw some conclusions about conserved positions. Many cysteine residues have been conserved, suggesting that vitellogenin structure has been maintained over a long evolutionary distance and is dependent upon disulfide bonds. In addition, a 20-residue segment shows conservation between the vertebrate and the nematode vitellogenins. This sequence may play a highly conserved role in vitellogenesis, such as specific recognition by oocytes. On the whole, however, selection may be acting more strongly on amino acid composition and codon usage than on amino acid sequence, as might be expected for abundant storage proteins: The amino acid compositions of vit-2, vit-5, and vit-6 products are remarkably similar, despite the fact that the sequence of the vit-2 protein is only 22% and 50% identical to the sequences of vit-6 and vit-5 proteins, respectively.
秀丽隐杆线虫的卵黄蛋白原由一个包含六个基因的家族编码，其中一个基因vit-5此前已被测序，并显示出与脊椎动物的卵黄蛋白原基因惊人地密切相关。在此，我们报告了蛙和鸡的卵黄蛋白原氨基酸序列与秀丽隐杆线虫三个基因（vit-5以及两个新测序的基因vit-2和vit-6）的氨基酸序列比对结果。vit-6的四个内含子位置与vit-5的四个内含子位置均不同，但这八个位置中的三个与脊椎动物卵黄蛋白原基因的内含子位置相同或相近。所编码的多肽彼此间差异足够大，使我们能够就保守位置得出一些结论。许多半胱氨酸残基得以保留，这表明卵黄蛋白原结构在漫长的进化过程中得以维持，且依赖于二硫键。此外，一个20个残基的片段在脊椎动物和线虫的卵黄蛋白原之间显示出保守性。该序列可能在卵黄发生过程中发挥高度保守的作用，比如卵母细胞的特异性识别。然而总体而言，正如对丰富的储存蛋白所预期的那样，选择作用于氨基酸组成和密码子使用的力度可能比对氨基酸序列的作用更强：尽管vit-2蛋白的序列与vit-6和vit-5蛋白的序列分别仅有22%和50%的同一性，但vit-2、vit-5和vit-6产物的氨基酸组成却非常相似。
