A double - strand cdna fragment of dh ( diapause hormone ) gene was obtained from kt - pcr amplification . the fragment was digested by two restriction enzyme nde 1 / ecor 1 and then was joined with pet - 30a ( + ) plasmid which was digested by nde 1 / ecor 1 too . then the outcome was transformed into escherichia coli bl21 Pcr产物经nde / ecor双酶切后，与同样双酶切的pet - 30a ( + )质粒连接并转化至大肠杆菌( escherichiacoli ) bl21中，经检测筛选，成功得到阳性克隆。
