Gmachl M, Kreil G
Institute of Molecular Biology, Austrian Academy of Sciences, Salzburg.
J Biol Chem. 1995 May 26;270(21):12704-8. doi: 10.1074/jbc.270.21.12704.
From a cDNA library prepared from venom glands of worker bees, clones encoding the precursors of apamin and MCD peptide have been isolated. The cDNAs are similar at the 5'-ends and identical in their 3'-regions. Analysis of the corresponding genes has revealed the existence of six exons separated by introns rich in A + T. Starting from the 5'-end, these exons are arranged in the following order: three exons of the mast cell-degranulating (MCD) peptide precursor, two exons of the gene for the apamin precursor, and finally a 3'-exon present in both cDNAs. This suggests that the bulk of the apamin gene resides in the third intron of the MCD peptide gene. Using inverse polymerase chain reaction, a segment of genomic DNA upstream of the first exon of the MCD precursor gene was obtained. The sequence of this segment shows 81% identity to the DNA sequence preceding the first exon of the apamin gene and both contain a putative TATA box. We thus propose that the mRNA encoding the apamin precursor originates from a primary transcript which starts in the third intron of the MCD peptide gene. Both cDNAs encode unusually small precursors comprising only 46 amino acids in case of apamin and 50 in the case of the MCD peptide.
从工蜂毒腺制备的cDNA文库中，已分离出编码蜂毒明肽和MCD肽前体的克隆。这些cDNA在5'端相似，在3'区域相同。对相应基因的分析表明，存在六个外显子，被富含A+T的内含子隔开。从5'端开始，这些外显子按以下顺序排列：肥大细胞脱颗粒（MCD）肽前体的三个外显子、蜂毒明肽前体基因的两个外显子，最后是两个cDNA中都存在的一个3'外显子。这表明蜂毒明肽基因的大部分位于MCD肽基因的第三个内含子中。使用反向聚合酶链反应，获得了MCD前体基因第一个外显子上游的一段基因组DNA。该片段的序列与蜂毒明肽基因第一个外显子之前的DNA序列有81%的同一性，并且都含有一个假定的TATA盒。因此，我们提出编码蜂毒明肽前体的mRNA起源于一个起始于MCD肽基因第三个内含子的初级转录本。两个cDNA都编码异常小的前体，蜂毒明肽的前体仅包含46个氨基酸，MCD肽的前体包含50个氨基酸。
