Fu Y H, Young J L, Marzluf G A
Department of Biochemistry, Ohio State University, Columbus 43210.
Mol Gen Genet. 1988 Sep;214(1):74-9. doi: 10.1007/BF00340182.
Expression of the structural genes of the nitrogen control circuit of Neurospora crassa is regulated by the positive-acting nit-2 control gene and by the negative-acting nmr control gene. Nitrate reductase is expressed in a constitutive fashion in nmr mutant strains, which appear to be largely insensitive to nitrogen catabolite repression. Thus, nmr mutants are sensitive to chlorate in the presence of ammonia or glutamine, whereas the wild type is chlorate resistant under these conditions. A cosmid library was screened for the presence of the nmr+ gene by the sib selection procedure, and a single cosmid was isolated which transforms the nmr mutant to chlorate resistance at a high frequency. A restriction fragment length polymorphism analysis revealed that the cloned DNA segment maps to the precise genomic location of nmr. Northern blot analyses revealed that the nmr gene is itself not regulated but is expressed constitutively to give a single transcript of approximately 1.8 kb.
粗糙脉孢菌氮控制回路结构基因的表达受正向作用的nit-2控制基因和负向作用的nmr控制基因调控。硝酸还原酶在nmr突变菌株中以组成型方式表达，这些菌株似乎对氮分解代谢物阻遏基本不敏感。因此，nmr突变体在有氨或谷氨酰胺存在时对氯酸盐敏感，而野生型在这些条件下对氯酸盐具有抗性。通过同胞选择程序筛选黏粒文库中是否存在nmr⁺基因，分离出一个单一黏粒，它能以高频将nmr突变体转化为对氯酸盐具有抗性。限制性片段长度多态性分析表明，克隆的DNA片段定位于nmr精确的基因组位置。Northern印迹分析表明，nmr基因本身不受调控，而是组成型表达，产生一个约1.8 kb的单一转录本。
