Tetracycline gene modification

Several gene dusters encoding the enzymes of polyketide synthesis have been cloned (partially or completely). Aromatic polyketides (e.g., tetracyclines, actinorho-dine, and anthracyclines) are synthesized by type II PKSs, which are multienzyme OMn-plexes similar to FAS type II (63). In contrast, the polyketide chain of mactolide antibiotics such as erythromycin and avermectin are synthesized by PKS type I, consisting of large multifunctional polypeptides similar to FAS type I but composed of repeated units or "modules" with each active site carrying out only one reaction in the assembly and modification of each carbon chain (64,65). 

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