Poulsen P, Jensen K F, Valentin-Hansen P, Carlsson P, Lundberg L G
Eur J Biochem. 1983 Sep 15;135(2):223-9. doi: 10.1111/j.1432-1033.1983.tb07641.x.
Orotate phosphoribosyltransferase (EC 2.4.2.10) was purified to electrophoretic homogeneity from a strain of Escherichia coli containing the pyrE gene cloned on a multicopy plasmid. The relative molecular masses (Mr) of the native enzyme and its subunit were estimated by means of gel filtration and electrophoresis in the presence of dodecyl sulfate. The amino acid sequences at the N and C termini, as well as the amino acid composition, were determined. The nucleotide sequence of the structural pyrE gene, including 394 nucleotide residues preceding the beginning of the coding frame, was also established. From the results the following conclusions may be drawn. Orotate phosphoribosyltransferase is a dimeric protein with subunits of Mr 23 326 consisting of 211 amino acid residues. The pyrE gene is transcribed in a counter-clock wise direction from the E. coli chromosome as an mRNA with a considerable leader segment in front of the protein-coding region. This leader contains a structure with features characteristic for a (translated?) rho-independent transcriptional terminator, which is preceded by a cluster of uridylate residues. This indicates that the frequency of pyrE transcription is regulated by an RNA polymerase (UTP) modulated attenuation.
乳清酸磷酸核糖基转移酶（EC 2.4.2.10）是从一株含有克隆在多拷贝质粒上的pyrE基因的大肠杆菌中纯化至电泳纯的。通过凝胶过滤和十二烷基硫酸钠存在下的电泳来估计天然酶及其亚基的相对分子质量（Mr）。测定了N端和C端的氨基酸序列以及氨基酸组成。还确定了结构pyrE基因的核苷酸序列，包括编码框起始之前的394个核苷酸残基。从这些结果可以得出以下结论。乳清酸磷酸核糖基转移酶是一种二聚体蛋白，其亚基Mr为23326，由211个氨基酸残基组成。pyrE基因从大肠杆菌染色体以逆时针方向转录为一种mRNA，在蛋白质编码区之前有一个相当长的前导序列。该前导序列包含一个具有（翻译后的？）不依赖ρ的转录终止子特征的结构，其前面有一簇尿苷酸残基。这表明pyrE转录频率受RNA聚合酶（UTP）调节的衰减作用调控。
