Jacquet M, Guilbaud R, Garreau H
Laboratoires de Biologie Expérimentale, Université de Paris-Sud, Orsay, France.
Mol Gen Genet. 1988 Mar;211(3):441-5. doi: 10.1007/BF00425698.
A Dictyostelium discoideum DNA fragment that complements the ura3 and the ura5 mutants of Saccharomyces cerevisiae has been sequenced. It contains an open reading frame of 478 codons capable of encoding a polypeptide of molecular weight 52475. This gene, named DdPYR5-6, encodes a bifunctional protein composed of the orotate phosphoribosyl transferase (OPRTase) and the orotidine-5'-phosphate decarboxylase (OMPdecase) domains described for UMP synthase in mammals. The existence of separate domains for the two activities was suspected because deletion of the N-terminal coding segment of the gene eliminated the ura5 but not the ura3 complementing activity. We have now confirmed that the two parts of the open reading frame share homology with known OPRTase and OMPdecase sequences. Several blocks of sequence are conserved among OPRTase from bacteria, fungi and slime mold and one of them corresponds to the consensus sequence for phosphoribosylbinding sites. The OMPdecase domain shows extensive similarity with the yeast and Neurospora crassa enzymes, suggesting that they have evolved from an ancestral gene which was fused to the OPRTase gene in D. discoideum. It is less related to the bacterial enzyme but all these sequences present conserved blocks of homology which could identify the active site. The codon usage is strongly biased in a manner similar to that found for other D. discoideum genes. The flanking DNA contains homopolymers of A and T and alternating sequences that are characteristic of the gene organization in D. discoideum.
已对一种能互补酿酒酵母ura3和ura5突变体的盘基网柄菌DNA片段进行了测序。它包含一个478个密码子的开放阅读框，能够编码分子量为52475的多肽。这个名为DdPYR5 - 6的基因编码一种双功能蛋白，该蛋白由哺乳动物UMP合酶中描述的乳清酸磷酸核糖基转移酶（OPRTase）和乳清苷 - 5'-磷酸脱羧酶（OMPdecase）结构域组成。由于该基因N端编码片段的缺失消除了ura5而非ura3的互补活性，因此怀疑这两种活性存在独立的结构域。我们现在已经证实，开放阅读框的两个部分与已知的OPRTase和OMPdecase序列具有同源性。细菌、真菌和黏菌的OPRTase之间有几个序列块是保守的，其中一个与磷酸核糖结合位点的共有序列相对应。OMPdecase结构域与酵母和粗糙脉孢菌的酶显示出广泛的相似性，这表明它们是从一个祖先基因进化而来的，该祖先基因在盘基网柄菌中与OPRTase基因融合。它与细菌酶的关系较小，但所有这些序列都存在保守的同源块，这些同源块可以确定活性位点。密码子使用情况存在强烈偏向性，其方式与在其他盘基网柄菌基因中发现的情况类似。侧翼DNA包含A和T的同聚物以及交替序列，这些是盘基网柄菌基因组织的特征。
