Nikkomycins,a competitive inhibitor of chitin synthase,are a group of peptidyl nucleoside antibiotics with potent fungicidal,insecticidal,and acaricidal activities To increase the yields of the nikkomycins in Streptomyces ansochromogenes,pSET152 carrying the whole nikkomycin gene cluster (35 kb) was constrtucted by combining the RED/ET technology with classic cloning procedures [1].The resulting plasmid (pNIK) was introduced into S.ansochromogenes by conjugal transfer [2].