Comparison of the primary sequences of ADS, AQS, and other type III PKSs. The secondary structures of ADS are delineated as follows: α-helices (rectangles) and β-strands (arrows). The Cys, His, and Asn catalytic triad and the residues lining the active-site cavity of CHS are colored red and blue, respectively. Tyr-215 in AQS and the corresponding residues in other type III PKSs are highlighted in green. GenBankTM accession numbers are as follows: MsCHS, L02902; CmQNS, AB823730; ClDCS, AB535216; ClCURS1, AB495007; OsCUS, BAC79571; RpBAS, AF326911; RdORS, LC133082. The sequence of HsPKS3 has not yet been released from GenBankTM.