Werner M, Feller A, Piérard A
Eur J Biochem. 1985 Jan 15;146(2):371-81. doi: 10.1111/j.1432-1033.1985.tb08663.x.
A yeast DNA fragment carrying the gene CP A1 encoding the small subunit of the arginine pathway carbamoyl-phosphate synthetase has been sequenced. Only one continuous coding sequence on this fragment was long enough to account for the presumed molecular mass of CP A1 protein product. It codes for a polypeptide of 411 amino acids having a relative molecular mass, Mr, of 45 358 and showing extensive homology with the product of carA, the homologous Escherichia coli gene. CP A1 and carA products are glutamine amidotransferases which bind glutamine and transfer its amide group to the large subunits where it is used for the synthesis of carbamoyl-phosphate. A comparison of the amino acid sequences of CP A1 polypeptide with the glutamine amidotransferase domains of anthranilate and p-amino-benzoate synthetases from various sources has revealed the presence in each of these sequences of three highly conserved regions of 8, 11 and 6 amino acids respectively. The 11-residue oligopeptide contains a cysteine which is considered as the active-site residue involved in the binding of glutamine. The distances (number of amino acid residues) which separate these homology regions are accurately conserved in these various enzymes. These observations provide support for the hypothesis that these synthetases have arisen by the combination of a common ancestral glutamine amidotransferase subunit with distinct ammonia-dependent synthetases. Little homology was detected with the amide transfer domain of glutamine phosphoribosyldiphosphate amidotransferase which may be the result of a convergent evolutionary process. The flanking regions of gene CP A1 have been sequenced, 803 base pairs being determined on the 5' side and 382 on the 3' side. Several features of the 5'-upstream region of CP A1 potentially related to the control of its expression have been noticed including the presence of two copies of the consensus sequence d(T-G-A-C-T-C) previously identified in several genes subject to the general control of amino acid biosynthesis.
一个携带编码精氨酸途径氨甲酰磷酸合成酶小亚基的基因CPA1的酵母DNA片段已被测序。该片段上只有一个连续的编码序列，其长度足以解释CPA1蛋白产物的推测分子量。它编码一个由411个氨基酸组成的多肽，相对分子质量Mr为45358，并且与同源的大肠杆菌基因carA的产物具有广泛的同源性。CPA1和carA产物是谷氨酰胺酰胺转移酶，它们结合谷氨酰胺并将其酰胺基团转移到大亚基上，用于合成氨甲酰磷酸。将CPA1多肽的氨基酸序列与来自不同来源的邻氨基苯甲酸和对氨基苯甲酸合成酶的谷氨酰胺酰胺转移酶结构域进行比较，发现这些序列中分别存在三个高度保守的区域，长度分别为8、11和6个氨基酸。这个11个残基的寡肽含有一个半胱氨酸，它被认为是参与谷氨酰胺结合的活性位点残基。在这些不同的酶中，分隔这些同源区域的距离（氨基酸残基数量）精确保守。这些观察结果支持了这样一种假说，即这些合成酶是由一个共同的祖先谷氨酰胺酰胺转移酶亚基与不同的氨依赖性合成酶组合而成的。与谷氨酰胺磷酸核糖焦磷酸酰胺转移酶的酰胺转移结构域几乎没有检测到同源性，这可能是趋同进化过程的结果。基因CPA1的侧翼区域已被测序，5'端测定了803个碱基对，3'端测定了382个碱基对。已经注意到CPA1 5'上游区域的几个可能与其表达调控相关的特征，包括在几个受氨基酸生物合成总体调控的基因中先前鉴定出的共有序列d(T-G-A-C-T-C)的两个拷贝的存在。
