稀有的黑檀体基因(ebony)5′UTR自发突变导致黑腹果蝇的黑条体突变

A rare spontaneous 5′ UTR deletion in ebony results in black strip mutation in Drosophila melanogaster

由于果蝇Drosophila群体中有很多自发突变其中包括多种体色突变,因此它是一个研究自发突变的优秀的模式体系。本研究证实我们实验室发现的一个可以引起果蝇体色突变的自发突变(bsr)是一个黑檀体(e)的等位基因,将其命名为ebsr。序列分析显示ebsr的5′端缺失了953个碱基,其中包括外显子1后端的206个碱基及相连的内含子1的747个碱基。逆转录PCR结果显示5′端的缺失导致内含子1不能从mRNA中剪接掉,由此导致该mRNA的翻译起始密码子AUG前端增加了一个3.2kb的序列。该序列导致ebsr的mRNA的5′UTR(5′-untranslated region)区较野生型基因增加近3kb的长度。通过mRNA二级结构分析发现这个增加的3kb的片段可以形成复杂的颈环结构(stem-loop)。免疫印迹结果显示该突变基因没有基因产物产生。本研究进一步证实了由于mRNA的5′UTR序列结构的改变可以影响到蛋白质的翻译。

Drosophila is an excellent model to study spontaneous mutation due to the availability of a large collection of spontaneous mutants, such as body pigment mutants. Previously, we found a spontaneous pigmentation mutant, bsr （black strip）, which was confirmed as an allele of ebony （e） and we named it as ebsr. Subsequent sequencing of genomic DNA revealed a deletion of 953 nucleotides at the 5＇ end of ebsr including 206 nucleotides of exon 1 and flanking 747 nucleotides of intron 1. Reverse-transcriptase PCR （ RT- PCR） showed that the deletion at the 5＇ end of ebsr leads to defective splicing, resulting in a transcriptional product with an additional 3.2 kb upstream of initiation codon AUG. RNA secondary structure analysis indicated that the unspliced 5＇ UTR folds into complex structure containing several more stem-loops than that of wild-type e. Western blotting results indicated that translation of e was totally suppressed in ebsr. This favors a model that the change of 5＇ UTR structure of mRNA prevents the protein translation.