Pitkin J, Davis R H
Department of Molecular Biology and Biochemistry, University of California, Irvine 92717.
Arch Biochem Biophys. 1990 May 1;278(2):386-91. doi: 10.1016/0003-9861(90)90275-4.
New mutations of the polyamine pathway of Neurospora crassa fell into three categories. The majority affected ornithine decarboxylase and lay at the previously defined spe-1 locus. One mutation, JP100, defining the new spe-2 locus, eliminated S-adenosyl-methionine decarboxylase and led to putrescine accumulation. Revertants of this mutation suggested that the locus encodes the enzyme. Two other mutations, LV105 and JP120, defined a third locus, spe-3. Strains with these mutations also accumulated putrescine and were presumed to lack spermidine synthase activity, which catalyzes the formation of spermidine from putrescine and decarboxylated S-adenosylmethionine. The three spe loci lay within about 20 map units of one another on the right arm of Linkage Group V in the order: centromere-spe-2-spe-1-spe-3. The requirement for spermidine for growth was much less in spe-2 and spe-3 mutants than in spe-1 mutants, which do not accumulate putrescine. This suggested that putrescine fulfills many, but not all, of the functions of spermidine, or that high levels of putrescine render spermidine more effective in its essential roles.
粗糙脉孢菌多胺途径的新突变可分为三类。大多数突变影响鸟氨酸脱羧酶，位于先前定义的spe-1位点。一个定义新spe-2位点的突变JP100消除了S-腺苷甲硫氨酸脱羧酶并导致腐胺积累。该突变的回复体表明该位点编码该酶。另外两个突变LV105和JP120定义了第三个位点spe-3。具有这些突变的菌株也积累腐胺，并推测缺乏亚精胺合酶活性，该酶催化由腐胺和脱羧S-腺苷甲硫氨酸形成亚精胺。这三个spe位点在连锁群V右臂上彼此相距约20个图距单位，顺序为：着丝粒-spe-2-spe-1-spe-3。与不积累腐胺的spe-1突变体相比，spe-2和spe-3突变体生长对亚精胺的需求要少得多。这表明腐胺履行了亚精胺的许多但不是全部功能，或者高水平的腐胺使亚精胺在其基本作用中更有效。
