Fogel S, Lax C, Hurst D D
Genetics. 1978 Nov;90(3):489-500. doi: 10.1093/genetics/90.3.489.
The his1 gene (chromosome V) of Saccharomyces cerevisiae specifies phosphoribosyl transferase (E.C.2.4.2.17), the first enzyme of histidine biosynthesis. This hexameric enzyme has both catalytic and regulatory functions. The spontaneous reversion rates of seven his1 mutations were studied. The reversion rates of the alleles at the proximal end of the locus (relative to the centromere) were about 50-fold higher than distal alleles. Spontaneous reversion to prototrophy was studied in diploids homoallelic for each of the seven his1 mutations. Based on tetrad analysis, the prototrophy revertants could be assigned to three classes: (1) revertant tetrads that carried a prototrophic allele indistinguishable from wild type; (2) revertant tetrads that carried a prototrophic allele characterized by histidine excretion and feedback resistance; and (3) revertant tetrads that did not contain a prototrophic spore, but rather a newly derived allele that complemented the original allele intragenically. Four of the seven his1 mutations produced the excretor revertant class, and two mutations produced the complementer revertant class. The significance of these findings to our understanding of gene organization and the catalytic and regulatory functions of gene products are discussed.
酿酒酵母的his1基因（位于第五条染色体）决定了磷酸核糖基转移酶（酶编号：2.4.2.17），这是组氨酸生物合成过程中的首个酶。这种六聚体酶兼具催化和调节功能。研究了七个his1突变的自发回复突变率。该基因座近端（相对于着丝粒）等位基因的回复突变率比远端等位基因高出约50倍。对这七个his1突变各自的纯合同等位基因二倍体进行了向原养型的自发回复突变研究。基于四分体分析，原养型回复体可分为三类：（1）携带与野生型无法区分的原养型等位基因的回复四分体；（2）携带以组氨酸排泄和反馈抗性为特征的原养型等位基因的回复四分体；（3）不含原养型孢子，而是含有一个新衍生的等位基因，该等位基因在基因内与原始等位基因互补的回复四分体。七个his1突变中有四个产生了排泄型回复体类别，两个突变产生了互补型回复体类别。讨论了这些发现对于我们理解基因组织以及基因产物的催化和调节功能的意义。
