Sorourian Mehran, Betrán Esther
Department of Biology, University of Texas at Arlington, TX, USA.
Fly (Austin). 2010 Jan-Mar;4(1):3-11. doi: 10.4161/fly.4.1.11136. Epub 2010 Jan 30.
Proteasomes are large multisubunit complexes responsible for regulated protein degradation. Made of a core particle (20S) and regulatory caps (19S), proteasomal proteins are encoded by at least 33 genes, of which 12 have been shown to have testis-specific isoforms in Drosophila melanogaster. Pros28.1A (also known as Prosalpha4T1), a young retroduplicate copy of Pros28.1 (also known as Prosalpha4), is one of these isoforms. It is present in the D. melanogaster subgroup and was previously shown to be testis-specific in D. melanogaster. Here, we show its testis-specific transcription in all D. melanogaster subgroup species. Due to this conserved pattern of expression in the species harboring this insertion, we initially expected that a regulatory region common to these species evolved prior to the speciation event. We determined that the region driving testis expression in D. melanogaster is not far from the coding region (within 272 bp upstream of the ATG). However, different Transcription Start Sites (TSSs) are used in D. melanogaster and D. simulans, and a "broad" transcription start site is used in D. yakuba. These results suggest one of the following scenarios: (1) there is a conserved motif in the 5' region of the gene that can be used as an upstream or downstream element or at different distance depending on the species; (2) different species evolved diverse regulatory sequences for the same pattern of expression (i.e., "TSS turnover"); or (3) the transcription start site can be broad or narrow depending on the species. This work reveals the difficulties of studying gene regulation in one species and extrapolating those findings to close relatives.
蛋白酶体是负责调控蛋白质降解的大型多亚基复合物。蛋白酶体由一个核心颗粒（20S）和调节帽（19S）组成，其蛋白质由至少33个基因编码，其中12个基因在黑腹果蝇中已被证明具有睾丸特异性异构体。Pros28.1A（也称为Prosalpha4T1）是Pros28.1（也称为Prosalpha4）的一个年轻的反转重复拷贝，是这些异构体之一。它存在于黑腹果蝇亚组中，先前已证明在黑腹果蝇中具有睾丸特异性。在这里，我们展示了它在所有黑腹果蝇亚组物种中的睾丸特异性转录。由于在具有这种插入的物种中存在这种保守的表达模式，我们最初预计这些物种共有的一个调控区域在物种形成事件之前就已经进化出来了。我们确定，在黑腹果蝇中驱动睾丸表达的区域离编码区不远（在ATG上游272 bp范围内）。然而，黑腹果蝇和拟暗果蝇使用不同的转录起始位点（TSS），而雅库布果蝇使用一个“宽泛”的转录起始位点。这些结果表明了以下几种情况之一：（1）基因的5'区域存在一个保守基序，根据物种的不同，它可以用作上游或下游元件，或者在不同距离处使用；（2）不同物种为相同的表达模式进化出了不同的调控序列（即“TSS转换”）；或者（3）转录起始位点根据物种的不同可以是宽泛的或狭窄的。这项工作揭示了在一个物种中研究基因调控并将这些发现外推到近亲物种时所面临的困难。
