Smith J M, Daum H A
J Biol Chem. 1987 Aug 5;262(22):10565-9.
5'-Phosphoribosylglycinamide transformylase (EC 2.1.2.2), encoded by the purN gene of Escherichia coli, catalyzes the synthesis of 5'-phosphoribosylformylglycinamide from 5'-phosphoribosylglycinamide (GAR). The mature protein, as deduced from the purN structural gene sequence, contains 212 amino acid residues and has a calculated Mr of 23,241. The purN gene is located adjacent to and immediately downstream from the purM gene encoding 5'-phosphoribosyl-5-aminoimidazole (AIR) synthetase where the initiation codon for GAR transformylase overlaps the termination codon of AIR synthetase. Based on polarity studies, the expression of the purN gene originates from the purM control region and thus forms a purMN operon. The E. coli GAR transformylase shows greater homology to the GAR transformylase domain of the trifunctional Gart polypeptide of Drosophila than to the single GAR transformylase of Saccharomyces. Immediately downstream from the purN gene of the purMN operon is a region of dyad symmetry capable of forming a hairpin stem and loop structure characteristic of a rho-independent terminator.
5'-磷酸核糖甘氨酰胺转甲酰基酶（EC 2.1.2.2）由大肠杆菌的purN基因编码，催化从5'-磷酸核糖甘氨酰胺（GAR）合成5'-磷酸核糖甲酰甘氨酰胺。根据purN结构基因序列推导，成熟蛋白含有212个氨基酸残基，计算所得的分子量为23241。purN基因位于编码5'-磷酸核糖-5-氨基咪唑（AIR）合成酶的purM基因相邻且紧挨着下游的位置，其中GAR转甲酰基酶的起始密码子与AIR合成酶的终止密码子重叠。基于极性研究，purN基因的表达源自purM控制区，因此形成一个purMN操纵子。大肠杆菌GAR转甲酰基酶与果蝇三功能Gart多肽的GAR转甲酰基酶结构域的同源性高于与酿酒酵母单一GAR转甲酰基酶的同源性。在purMN操纵子的purN基因紧邻下游是一个具有二重对称的区域，能够形成发夹茎环结构，这是不依赖ρ因子的终止子的特征。
