A phylogram illustrating the clustering of ACP domains into subfamilies. The first 10 ACPs are from modular polyketide synthases: either erythromycin PKS (labeled DebsACP) or rifamycin PKS (labeled RifACP). The ACP domains from fatty acid synthases (E. coli ACP and B. subtilis ACP) form a distinct subgroup. In turn, the actinorhodin (act), frenolicin (fren), and oxytetracycline (otc) ACPs, which originate from type II (aromatic) polyketide synthases, also form a subfamily distinct both from the ACP domains of the fatty acid synthase origin and from the ACPs that belong to modular polyketide synthases. The sequences were aligned using PileUp program (GCG SeqWeb software package, Accelrys Inc.) and the phylogram was produced using the CLUSTAL W server at the European Bioinformatics Institute (www.ebi.ac.uk/clustalw/).