Gelsthorpe M, Pulumati M, McCallum C, Dang-Vu K, Tsubota S I
Department of Biology, Saint Louis University, MO 63103, USA.
Gene. 1997 Feb 28;186(2):189-95. doi: 10.1016/s0378-1119(96)00701-9.
The enhancer of rudimentary gene, e(r), in Drosophila melanogaster encodes a protein, ER, whose function has been implicated in pyrimidine biosynthesis and the cell cycle (Wojcik et al. (1994) Genetics 138, 1163-1170). In order to identify conserved regions of the protein and potentially important functional domains, the e(r) gene was cloned and sequenced from two other insects (Drosophila virilis and Aedes aegypti) and three vertebrates (Homo sapiens, Mus musculus, and Brachydanio rerio) and sequenced from a flowering plant (Arabidopsis thaliana). These sequences along with those of a nematode (Caenorhabditis elegans) exhibit a high degree of identity. ER of Drosophila melanogaster is 76% identical to the three vertebrate proteins, 49% identical to the nematode protein, and 40% identical to the plant protein. There is high evolutionary conservation among the vertebrates. The mouse and human proteins are identical and differ from that of the zebrafish by a single conservative amino-acid change (valine for isoleucine). A dramatic sequence conservation is seen in the position of the hydrophobic amino acids. Of the 27 positions occupied by hydrophobic amino acids in ER of Drosophila melanogaster, 25 of the corresponding positions in the human protein, 23 of the positions in Caenorhabditis elegans, and 20 of the positions in Arabidopsis thaliana have hydrophobic amino acids. Most of these residues are present in three conserved amphipathic alpha-helices, which are proposed to function in protein-protein interactions. Two phosphorylation sites for casein kinase II (CKII) have also been conserved within the animal groups. Purified ER from Drosophila melanogaster is phosphorylated in vitro by CKII, arguing that these two sites are functional in vivo. A putative shift in the secondary structure of ER caused by the phosphorylation of these sites suggests that CKII may be regulating the activity of the ER in vivo.
果蝇中原始基因的增强子e(r)编码一种蛋白质ER，其功能与嘧啶生物合成和细胞周期有关（Wojcik等人，(1994)《遗传学》138卷，1163 - 1170页）。为了确定该蛋白质的保守区域和潜在的重要功能结构域，从另外两种昆虫（果蝇和埃及伊蚊）、三种脊椎动物（人类、小鼠和斑马鱼）中克隆并测序了e(r)基因，还从一种开花植物（拟南芥）中进行了测序。这些序列与线虫（秀丽隐杆线虫）的序列具有高度的同一性。黑腹果蝇的ER与三种脊椎动物蛋白质的同一性为76%，与线虫蛋白质的同一性为49%，与植物蛋白质的同一性为40%。脊椎动物之间存在高度的进化保守性。小鼠和人类的蛋白质相同，与斑马鱼的蛋白质仅在一个保守氨基酸变化（异亮氨酸变为缬氨酸）上有所不同。在疏水氨基酸的位置上可以看到显著的序列保守性。在黑腹果蝇ER中由疏水氨基酸占据的27个位置中，人类蛋白质中相应位置有25个、秀丽隐杆线虫中有23个、拟南芥中有20个位置存在疏水氨基酸。这些残基大多存在于三个保守的两亲性α螺旋中，推测其在蛋白质 - 蛋白质相互作用中发挥作用。在动物类群中，酪蛋白激酶II（CKII）的两个磷酸化位点也得到了保守。从黑腹果蝇中纯化的ER在体外可被CKII磷酸化，这表明这两个位点在体内具有功能。这些位点磷酸化导致的ER二级结构的假定变化表明CKII可能在体内调节ER的活性。
