Gardner W J, Woods R A
Can J Microbiol. 1979 Mar;25(3):380-9. doi: 10.1139/m79-059.
Mutants of yeast which are auxotrophic for guanine have been isolated from two prototrophic haploid strains, one of which carried the suppressor of purine excretion, su-pur, and the other carried the alternative allele, su-pur+. The mutants were allocated to three genes, gual, gua2, and gua3, between which no close linkage was demonstrable. Mutants of all three genes were recessive and showed normal Mendelian segregation in crosses. The gene gual was shown by an in vivo enzyme assay procedure to specify guanosine 5'-phosphate (GMP) synthetase, the second enzyme involved in the biosynthesis of GMP from inosine 5'-phosphate (IMP). Mutants of this gene excrete large amounts of purine derivatives, predominantly xanthosine, into guanine-free, but not into guanine-supplemented, medium. The gene gau2 is probably involved in the biosynthesis of riboflavin from guanine nucleotides; the phenotype of these mutants suggests a possible interaction between aromatic amino acid metabolism and riboflavin biosynthesis. No role for gua3 can be assigned on the evidence so far available, but it is not involved in the specification of IMP dehydrogenase, the first enzyme involved in the synthesis of GMP and IMP.
已从两个原养型单倍体菌株中分离出对鸟嘌呤营养缺陷的酵母突变体，其中一个携带嘌呤排泄抑制因子su-pur，另一个携带其等位基因su-pur+。这些突变体被定位到三个基因gual、gua2和gua3上，它们之间未显示出紧密连锁。所有这三个基因的突变体都是隐性的，并且在杂交中表现出正常的孟德尔分离。通过体内酶测定程序表明，基因gual指定鸟苷5'-磷酸（GMP）合成酶，这是从肌苷5'-磷酸（IMP）生物合成GMP过程中的第二种酶。该基因的突变体在不含鸟嘌呤但添加了鸟嘌呤的培养基中会向培养基中大量排泄嘌呤衍生物，主要是黄苷。基因gau2可能参与从鸟嘌呤核苷酸生物合成核黄素；这些突变体的表型表明芳香族氨基酸代谢与核黄素生物合成之间可能存在相互作用。根据目前可得的证据，无法确定gua3的作用，但它不参与指定IMP脱氢酶，IMP脱氢酶是合成GMP和IMP过程中的第一种酶。
