REPOSITIONING OF A DOMAIN IN A MODULAR POLYKETIDE SYNTHASE TO PROMOTESPECIFIC CHAIN CLEAVAGE

Macrocyclic polyketides exhibit an impressive range of medically usefu l activities, and there is great interest in manipulating the genes th at govern their synthesis. The 6-deoxyerythronolide B synthase (DEBS) of Saccharopolyspora erythraea, which synthesizes the aglycone core of the antibiotic erythromycin A, has been modified by repositioning of a chain-terminating cyclase domain to the carboxyl-terminus of DEBS1, the multienzyme that catalyzes the first two rounds of polyketide chai n extension. The resulting mutant markedly accelerates formation of th e predicted triketide lactone, compared to a control in which the repo sitioned domain is inactive. Repositioning of the cyclase should be ge nerally useful for redirecting polyketide synthesis to obtain polyketi des of specified chain lengths.