Martin P F, Place A R, Pentz E, Sofer W
J Mol Biol. 1985 Jul 20;184(2):221-9. doi: 10.1016/0022-2836(85)90375-4.
A mutant gene, which we have designated AdhnB, codes for a defective form of the enzyme alcohol dehydrogenase in Drosophila melanogaster. We show that the polypeptide encoded by AdhnB is approximately 2000 Mr smaller than the protein synthesized under the direction of the wild-type alcohol dehydrogenase gene. In contrast, the alcohol dehydrogenase mRNA produced by both genes is the same size. We cloned and sequenced a portion of the protein-coding region of AdhnB and compared it to the same region in the wild-type gene. We found a single base substitution: a change of the TGG tryptophan codon at amino acid 235 to a TGA termination codon. This nonsense mutation accounts for the observed reduction in size of the alcohol dehydrogenase polypeptide. In further studies, we found that the steady-state levels of alcohol dehydrogenase mRNA in flies carrying the AdhnB gene and the wild-type alcohol dehydrogenase gene were indistinguishable. However, the steady-state level of alcohol dehydrogenase polypeptide was reduced to 1% of wild-type levels in flies with the AdhnB gene. Moreover, the rate of alcohol dehydrogenase synthesis in mutant flies was reduced to 50% of that found in wild type. The aberration in AdhnB thus affects both the rate of synthesis and the rate of degradation of the alcohol dehydrogenase peptide. AdhnB is the first reported nonsense mutant in Drosophila.
我们命名为AdhnB的一个突变基因编码果蝇中一种有缺陷形式的乙醇脱氢酶。我们发现，AdhnB编码的多肽比野生型乙醇脱氢酶基因指导合成的蛋白质小约2000道尔顿。相比之下，这两个基因产生的乙醇脱氢酶mRNA大小相同。我们克隆并测序了AdhnB蛋白质编码区的一部分，并将其与野生型基因的相同区域进行比较。我们发现了一个单碱基替换：第235位氨基酸处的TGG色氨酸密码子变为TGA终止密码子。这种无义突变解释了观察到的乙醇脱氢酶多肽大小的减小。在进一步的研究中，我们发现携带AdhnB基因的果蝇和野生型乙醇脱氢酶基因的果蝇中，乙醇脱氢酶mRNA的稳态水平没有差异。然而，携带AdhnB基因的果蝇中乙醇脱氢酶多肽的稳态水平降至野生型水平的1%。此外，突变果蝇中乙醇脱氢酶的合成速率降至野生型的50%。因此，AdhnB中的畸变影响了乙醇脱氢酶肽的合成速率和降解速率。AdhnB是果蝇中首次报道的无义突变体。
