Maitra P K, Lobo Z
Genetics. 1983 Nov;105(3):501-15. doi: 10.1093/genetics/105.3.501.
Mutants of Saccharomyces cerevisiae lacking glucokinase (EC 2.7.1.2) have no discernible phenotypic difference from the wild-type strain; in a hexokinaseless background, however, they are unable to grow on any sugar except galactose. Reversion studies with glucokinase mutants indicate that the yeast S. cerevisiae has no other enzyme for phosphorylating glucose except the two hexokinases, P1 and P2, and glucokinase. Spontaneous revertants of hxk1 hxk2 glk1 strains collected on glucose regain any one of these three enzymes. The majority of glucokinase revertants synthesize species of enzyme activity that are kinetically or otherwise indistinguishable from the wild-type enzyme. In a few cases the reverted enzyme is very perceptibly altered in properties with a Km for glucose two orders of magnitude higher than that of the enzyme from the wild-type parent. These recessive, noncomplementing mutants, thus, define a single structural gene GLK1 of glucokinase. Yeast diploids lacking all of the three enzymes for glucose phosphorylation fail to sporulate. Heterozygosity of either of the hexokinase genes HXK1 or HXK2, but not GLK1, restores sporulation. The location of GLK1 on chromosome III was indicated by loss of this chromosome when hexokinaseless diploids heterozygous for glk1 were selected for resistance to 2-deoxyglucose; the homologue of chromosome III carrying GLK1, the mating-type allele and other nutritional markers on this chromosome was lost. Meiotic mapping of glucokinase executed with heterozygosity of one of the hexokinases indicated that the gene GLK1 defining the structure of glucokinase protein is located on the left arm of chromosome III 24 cM to the left of his4 in the order: leu2--his4--glk1. --Only two of 206 independent glucokinase mutants are nonsense ochre, both of which map at one end of the gene. In hxk1 only one of 130 isolates is a nonsense mutation, whereas in hxk2 none has been found among 220 independent mutants. These results raise the possibility that the protein products of these genes have some other essential function. --An earlier mapping result for hxk2 has been corrected. The new location is on the left arm of chromosome VII, 17 cM distal to ade5 in the order: lys5--ade5--hxk2.
缺乏葡萄糖激酶（EC 2.7.1.2）的酿酒酵母突变体与野生型菌株没有明显的表型差异；然而，在缺乏己糖激酶的背景下，它们除了半乳糖外无法在任何糖类上生长。对葡萄糖激酶突变体的回复突变研究表明，酿酒酵母除了两种己糖激酶P1和P2以及葡萄糖激酶外，没有其他用于磷酸化葡萄糖的酶。在葡萄糖上收集的hxk1 hxk2 glk1菌株的自发回复突变体重新获得了这三种酶中的任何一种。大多数葡萄糖激酶回复突变体合成的酶活性种类在动力学或其他方面与野生型酶无法区分。在少数情况下，回复突变后的酶性质明显改变，其对葡萄糖的Km值比野生型亲本的酶高两个数量级。因此，这些隐性的、非互补的突变体定义了葡萄糖激酶的一个单一结构基因GLK1。缺乏所有三种葡萄糖磷酸化酶的酵母二倍体无法形成孢子。己糖激酶基因HXK1或HXK2中的任何一个杂合，但GLK1不杂合，可恢复孢子形成。当选择对2-脱氧葡萄糖有抗性的glk1杂合的无己糖激酶二倍体时，由于第三条染色体的丢失表明GLK1位于第三条染色体上；携带GLK1的第三条染色体的同源物、交配型等位基因以及该染色体上的其他营养标记丢失。用其中一种己糖激酶杂合进行的葡萄糖激酶减数分裂定位表明，定义葡萄糖激酶蛋白质结构的基因GLK1位于第三条染色体的左臂上，在his4左侧24 cM处，顺序为：leu2--his4--glk1。——206个独立的葡萄糖激酶突变体中只有两个是无义赭石突变，两者都位于基因的一端。在hxk1中，130个分离株中只有一个是无义突变，而在hxk2中，220个独立突变体中未发现无义突变。这些结果增加了这些基因的蛋白质产物具有其他某种基本功能的可能性。——hxk2的早期定位结果已得到纠正。新位置在第七条染色体的左臂上，在ade5远端17 cM处，顺序为：lys5--ade5--hxk2。
