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Rapamycin is one of triene macrolide antibiotics.It is used in clinics as a potent immunosuppressant with antifungal and antitumor activities.Studies on rapamycin biosynthesis (rap) and genetics have focused nearly exclusively on the mycelial actinomycete,Streptomyces hygroscopicus NRRL 5491.The other kind of actinomycete,Actinoplanes sp.N902-l09,however also produces rapamycin.The focus here was the cloning,characterization of the rapamycin cluster from Actinoplanes with respect to the already well characterized rapamycin gene cluster from Streptomyces hygroscopicus.The partial rapamycin-biosynthetic gene cluster of Actinoplanes was cloned and characterized.The 22.7-kb cluster contains 3 rap genes.Homologues were found for each gene in the previously characterized rap gene cluster from Streptomyces hygroscopicus.In addition,the gene order of the two rap clusters was conserved.This result showed that large gene sequence differences exist between two rapamycin biosynthetic gene clusters from two strain.