酿酒酵母(Saccharomyces cerevisiae)半乳糖可诱导表达系统特性的研究

把大肠杆菌β-半乳糖苷酶基因克隆到带有酵母半乳糖可诱导启动子GAL1的穿梭表达质粒pYESZ中，并把得到的重组质粒分别转化到两种不同遗传性状的宿主菌中，其中一株菌为蛋白酶活性缺失90％以上的pep4－3突变菌株。通过比较两株重组菌产生的β-半乳糖苷酶活性水平发现在所述实验条件下，蛋白酶缺失突变菌株中产生的β-卜半乳糖苷酶活水平不仅均要高于另一对照菌株，并且pep4-3突变菌株表现出受葡萄糖阻遏的严紧程度高及对诱导反应迅速等特点。此外，带有重组质粒的pep4－3突变菌株在葡萄糖阻遏培养基中最大生长量和重组对照菌株基本相同，但β-半乳糖苷酶在pep4－3突变菌株中的表达对细胞生长的影响明显小于对照菌株。

CHARACTERIZATION OF THE GALACTOSE-INDUCIBLE EXPRESSION SYSTEM IN SACCHAROMYCES CEREVISIAE

The β-galactosidase gene from E. colt was cloned into a E. coli-yeastshuttle vector PYES2 which cAnes the galactose-inducible promoter GALl. Theresulting recombinant plasmid was transformed into yeast host strains with differentgenetic background, one of which is a PeP4-3 mutant strain with at least 90%reduced achvity of the four vacuolar proteinases. By comparing the activity of theLacZ gene product (β-galactosidase), we found that under almost all test conditionsthe -galactosidase activity was higher in strain PeP4-3 than that in strain YTI.Moreover the peak-3 mutant strain exhibited tighter degree of repression by glucoseand more sensitive response to the induction and the continual expression of the galactosidase exerted less effect on the cell growth of peap4-3 much strain.