β－内酰胺酶启动子C－17缺失对其强度的影响

Effects of C-17 Deletion in theSpacer on theStrength of β-Lactainase Gene Promoter. SunNaien,

通过酶学手段在β－内酰胺酶启动子间隔序列中造成Ｃ－１７的缺失突变．以氨苄青霉素（Ａｍｐ）为底物，检测突变前后β－内酰胺酶活力变化，并作了细菌的Ａｍｐ耐受性试验，实验结果表明，Ｃ－１７的缺失突变使启动子强度增加约６０％，含有突变启动子的细菌对Ａｍｐ的抗性明显增强．突变体生长的半抑制浓度为２８０μｇ／ｍｌ，而在此浓度下野生型菌体吸光度只有突变体的５０％左右，对启动子强度增加的原因进行了讨论．

he C : G base-pair at position -17 in thespacer of β-lactamase gene promoter was re-moved by restriction with BspH Ⅰ. partial fill-ing-in with Klenow fragment, and trimmingwith niung bean nuclease. The β-lactamase ac-tivities of both bacteria harboring the wild-type and C-17 deleted plasmids were deter-mined using ampicillin as substrate. and thetolerances of the bacteria to ampicillin weretested. The results indicate that the C-17deletion increases the promoter strength byabout 60%. The mutant has more resistanceto ampicillin. The half-inhibition concentra-tion of ampicillin for the mutant growth is280μg/ml. At the same concentration. thewild-type cell density is only about half asmuch as that of the mutant. The causes forthe promoter-up mutation were discussed.