Domain organization and sequence comparison between bona fide PKSs for 9-membered (1–3) and 10-membered (6–8) enediyne core structures. Domain designations: KS, ketosynthase; AT, acyltransferase; ACP, putative acyl carrier protein; KR, ketoreductase; DH, dehydratase; TD, terminal domain (possibly containing a phosphopantetheinyl transferase).